Transmitter, receiver, communication apparatus, communication method and communication system

ABSTRACT

Digital data which are transmitted from a plurality of external devices to execute data exchange at their natural communication speeds respectively via a data transfer line are multiplexed, and multiplexed digital data are transmitted to an external network. The multiplexed digital data received from the external network are distributed by inverse multiplexing, and distributed digital data are received by target external devices via the data transfer line. Accordingly, the digital data having different communication speeds mutually can be communicated via a common data transfer line.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a transmitter, a receiver, acommunication apparatus, and a communication method capable of executinga centralization process of digital data by concentrating the digitaldata, which being transmitted from a plurality of external devices whichenable execution of data exchange at their natural transmission speedsrespectively or being transmitted from an external network, to a commondata transfer line, a common multiplexer, or a common distributor, andalso capable of implementing smooth two-way communications between theexternal network and the plurality of external devices or between theplurality of external devices.

The present invention also relates to a communication system constructedby connecting a plurality of communication apparatuses via a datatransmission line to execute data exchange between the plurality ofcommunication apparatuses and, more particularly, a communication systemcapable of implementing smooth two-way communications between theplurality of communication apparatuses.

The present invention also relates to a communication system constructedby connecting a plurality of communication apparatuses, to which oneexternal device or more than two external devices being connectedrespectively, via a data transmission line to execute data exchangebetween any external devices, between any communication apparatuses, orbetween any external device and any communication apparatus and, moreparticularly, a communication method and a communication system capableof improving a communication efficiency remarkably by avoiding surelycollision between communication data.

2. Description of the Prior Art

As protocols for communication devices or apparatuses commonly used inthe prior art, D2B (Audio, video and audiovisual systems DomesticDigital Bus: CIE/IEC 1030) employed to transmit digital audio data,etc.; standard which conforms to a recommendation made by CCITT(International Telegraph and Telephone Consulting Committee) and is usedto execute personal computer communication, etc.; USB (Universal SerialBus) and IEEE1394 used to connect personal computer peripheral devicessuch as a keyboard, a CRT display, a mouse, a modem, and a printer to apersonal computer main body; ATAPI (AT Attachment Packet Interface) usedas an interface to connect devices such as a DVD (Digital Video Disc orDigital Versatile Disc)-ROM drive, or a music CD (Compact Disc) player;MPEG2 (Moving Picture Image Coding Experts Group Phase2: ISO/IEC13818)which is a full color moving picture compression scheme for a digital TVset, etc.; ATM (Asynchronous Transfer Mode) for a computer and a digitalTV set; and the like, for example, have been known.

In recent, there has been caused a request to implement a centralizationprocess by concentrating sound data or video data supplied from variousvehicle-equipped devices such as a radio, a mobile telephone, a TV set,a CD player, a navigation system; speed data supplied from a speedsensor; moving orientation data supplied from a geomagnetism sensor;data of running conditions of the vehicle such as the distance databetween own vehicle and the next vehicle ahead running in the samedirection, and the like. The reason for such centralization process isthat, if such centralization process can be executed by concentratingoutput data supplied from various vehicle-equipped devices, varioussensors, and forth arranged in various locations of the vehicle, mutualoutput data can be commonly used by respective vehicle-equipped devices,and simultaneously necessary data can be communicated at once when anvehicle-vehicle communication to execute data communication between ownvehicle and another vehicle and a road-vehicle communication to executedata communication between own vehicle and stations arranged along therunning route should be conducted, so that convenience of the vehiclecan be improved.

With the above mentioned protocols, communication speeds, data formats,etc. have been specified individually according to respective protocolswithout regard to compatibility or interchangeability of communicationsin the existing circumstances. Accordingly, in the event that datacommunication should be executed between the vehicle-equipped deviceswhich have mutually different protocols respectively, for example, ingeneral personal computers in which an interface and a communicationcontrol unit both being constructed to enable communications betweenobject protocols are built in previously have been connected torespective vehicle-equipped devices and then personal computercommunications through such personal computers have been carried out.

However, in such data communications between the vehicle-equippeddevices, there have been many limitations to construct a system, e.g.,the personal computers have to be connected to respectivevehicle-equipped devices. Such many limitations have made it difficultto improve flexibility of the system and have become obstacles toconstruction of the communication system such as the vehicle-vehiclecommunication or the road-vehicle communication for which thecentralization process of data is requested.

SUMMARY OF THE INVENTION

The present invention has been made in view of the above circumstances,and it is an object of the present invention to provide a transmitter, areceiver, a communication apparatus, and a communication method capableof executing a centralization process of digital data by concentratingthe digital data, which being transmitted from a plurality of externaldevices which can execute data exchange at their natural transmissionspeeds respectively or being transmitted from an external network, to acommon data transfer line, a common multiplexer, or a commondistributor, and also capable of implementing smooth two-waycommunications between the external network and the plurality ofexternal devices.

Further, it is another object of the present invention to provide acommunication system capable of implementing smooth two-waycommunications between any communication apparatuses in thecommunication system which is constructed by connecting a plurality ofcommunication apparatuses via a data transmission line.

Furthermore, it is still another object of the present invention toprovide a communication method and a communication system capable ofimproving a communication efficiency remarkably by avoiding collisionbetween communication data surely when data exchange are executedbetween any external devices, between any communication apparatuses, orbetween any external device and any communication apparatus in thecommunication system which is constructed by connecting a plurality ofcommunication apparatuses, to which one external device or more than twoexternal devices being connected respectively, via a data transmissionline.

In order to achieve the above objects, there is provided a transmittercomprising a data transfer line for transferring digital data; aplurality of interfaces connected to a plurality of external devices inone-by-one correspondence, and constructed so as to fit to transmissionspeeds peculiar to the plurality of external devices respectively; aplurality of frequency modulators connected to the plurality ofinterfaces in one-by-one correspondence, for executing a frequencymodulation to synchronize the digital data which have naturaltransmission speeds on respective interfaces with a predetermined systemclock on the data transfer line, and then sending out the digital datawhich are subjected to the frequency modulation to the data transferline respectively; a multiplexer for multiplexing the digital data whichare transmitted from the plurality of frequency modulators via the datatransfer line in synchronism with the predetermined system clock, andthen transmitting multiplexed digital data to an external network; and aclock generator for generating reference clocks including thepredetermined system clock, and then supplying the reference clocks tothe plurality of frequency modulators and the multiplexer respectively.

According to the present invention, first, in a plurality of frequencymodulators, the frequency modulation is executed to synchronize thedigital data which have natural transmission speeds on respectiveinterfaces with a predetermined system clock on the data transfer line,and then the frequency-modulated digital data are sent out to the datatransfer line respectively. Then, the multiplexer multiplexes thedigital data which are transmitted from the plurality of frequencymodulators via the data transfer line in synchronism with thepredetermined system clock, and then transmits the multiplexed digitaldata to the external network.

Therefore, a centralization process of digital data can be executed byconcentrating the digital data, which being transmitted from a pluralityof external devices which can execute data exchange at their naturaltransmission speeds respectively, onto the common data transfer line.The digital data can also be multiplexed and then the multiplexeddigital data can be transmitted to the external network.

In order to achieve the above object, there is provided a receivercomprising a data transfer line for transferring digital data; adistributor for receiving multiplexed digital data transmitted from anexternal network, and then distributing the multiplexed digital data byinverse multiplexing insynchronism with a predetermined system clock onthe data transfer line to send out to the data transfer line; aplurality of interfaces connected to a plurality of external devices inone-by-one correspondence, and constructed so as to fit to transmissionspeeds peculiar to the plurality of external devices respectively; aplurality of frequency demodulators for receiving digital data outputfrom the distributor via the data transfer line, then executing afrequency demodulation to synchronize input data which have beensynchronized with the predetermined system clock on the data transferline with the natural transmission speeds on the plurality of interfacesrespectively, and then sending out the digital data which are subjectedto the frequency demodulation to the plurality of interfacesrespectively; and a clock generator for generating reference clocksincluding the predetermined system clock, and then supplying thereference clocks to the distributor and the plurality of frequencydemodulators respectively.

According to the present invention, first, in the distributor,multiplexed digital data transmitted from an external network arereceived, and then the multiplexed digital data are distributed byinverse multiplexing in synchronism with the predetermined system clockon the data transfer line to send out to the data transfer line. Then,the plurality of frequency demodulators receive the digital data outputfrom the distributor via the data transfer line, then execute thefrequency demodulation to synchronize input data which have beensynchronized with the predetermined system clock on the data transferline with the natural transmission speeds on the plurality of interfacesrespectively, and then send out the digital data which are subjected tothe frequency demodulation to the plurality of interfaces respectively.The plurality of external devices then receive the digital data via theplurality of interfaces.

Accordingly, since the multiplexed digital data transmitted from theexternal network are distributed to respective digital data by inversemultiplexing to send out to the data transfer line, the centralizationprocess of digital data can be executed by concentrating the digitaldata, and also respective external devices can receive respectivedigital data by transforming the digital data into data formats havingcommunication speeds peculiar to the plurality of interfaces.

In order to achieve the above object, there is provided a communicationapparatus comprising a data transfer line for transferring digital data;a distributor for receiving multiplexed digital data transmitted from anexternal network, and then distributing the multiplexed digital data byinverse multiplexing in synchronism with a predetermined system clock onthe data transfer line to send out to the data transfer line; aplurality of interfaces connected to a plurality of external devices inone-by-one correspondence, and constructed so as to fit to transmissionspeeds peculiar to the plurality of external devices respectively; aplurality of frequency modulators connected to the plurality ofinterfaces in one-by-one correspondence, for executing a frequencymodulation to synchronize the digital data which have naturaltransmission speeds on respective interfaces with a predetermined systemclock on the data transfer line, and then sending out the digital datawhich are subjected to the frequency modulation to the data transferline respectively; a plurality of frequency demodulators for receivingthe digital data output from the distributor via the data transfer line,then executing a frequency demodulation to synchronize input digitaldata which have been synchronized with the predetermined system clock onthe data transfer line with the natural transmission speeds on theplurality of interfaces respectively, and then sending out the digitaldata which are subjected to the frequency demodulation to the pluralityof interfaces respectively; a multiplexer for multiplexing the digitaldata which are transmitted from the plurality of frequency modulatorsvia the data transfer line in synchronism with the predetermined systemclock, and then transmitting multiplexed digital data to an externalnetwork; and a clock generator for generating reference clocks includingthe predetermined system clock, and then supplying the generatedreference clocks to the distributor, the multiplexer, the plurality offrequency modulators, and the plurality of frequency demodulatorsrespectively.

According to the present invention, when the digital data transmittedfrom the plurality of external devices respectively are transmitted tothe external network via the data transfer line, in the plurality offrequency modulators, the frequency modulation is executed tosynchronize the digital data which have natural transmission speeds onrespective interfaces with the predetermined system clock on the datatransfer line, and then the frequency-modulated digital data are sentout to the data transfer line respectively. Then, the multiplexermultiplexes the digital data which are transmitted via the data transferline in synchronism with the predetermined system clock and thentransmits the multiplexed digital data to the external network.

Meanwhile, when the multiplexed digital data transmitted from theexternal network are received by the plurality of external devices viathe data transfer line respectively, in the distributor, the multiplexeddigital data transmitted from the external network are received, andthen the multiplexed digital data are distributed by inversemultiplexing in synchronism with the predetermined system clock on thedata transfer line to send out to the data transfer line. Then, theplurality of frequency demodulators receive the digital data output fromthe distributor via the data transfer line, then execute the frequencydemodulation to synchronize input digital data which have beensynchronized with the predetermined system clock on the data transferline with the natural transmission speeds on the plurality of interfacesrespectively, and then sending out the frequency-demodulated digitaldata to the plurality of interfaces respectively. The digital data arethen received by the plurality of external devices via the plurality ofinterfaces respectively.

Accordingly, the centralization process of digital data can be executedby concentrating the digital data which being transmitted from theplurality of external devices which can execute data exchange at theirnatural communication speeds or being transmitted from the externalnetwork, and also two-way communications between the external networkand the plurality of external devices can be carried out smoothly.

In order to achieve the above object, there is provided a communicationmethod for use in a communication system including a data transfer linefor transferring digital data, and a plurality of interfaces connectedto a plurality of external devices in one-by-one correspondence, andconstructed so as to fit to transmission speeds peculiar to theplurality of external devices respectively, the communication methodcomprising the steps of: executing a frequency modulation to synchronizethe digital data which are output from the plurality of external deviceshaving natural transmission speeds on the plurality of interfacesrespectively with a predetermined system clock on the data transferline, and then sending out the digital data which are subjected to thefrequency modulation to the data transfer line respectively; andmultiplexing the digital data which are input via the data transfer linerespectively in synchronism with the predetermined system clock, andthen transmitting multiplexed digital data to an external network;whereby the digital data transmitted from the plurality of externaldevices respectively are sent to the external network via the datatransfer line, and receiving multiplexed digital data transmitted fromthe external network, and then distributing the multiplexed digital databy inverse multiplexing in synchronism with the predetermined systemclock to send out to the data transfer line; receiving the digital datatransmitted via the data transfer line respectively, and then executinga frequency demodulation to synchronize the digital data which have beensynchronized with the predetermined system clock with the naturaltransmission speeds on the plurality of interfaces respectively; andreceiving the digital data which are subjected to the frequencydemodulation by the plurality of external devices via the plurality ofinterfaces respectively; whereby the multiplexed digital datatransmitted from the external network are received by the plurality ofexternal devices via the data transfer line respectively.

According to the present invention, when the digital data transmittedfrom the plurality of external devices respectively are sent to theexternal network via the data transfer line, the frequency modulation isexecuted to synchronize the digital data which are output from theplurality of external devices having their natural transmission speedson the plurality of interfaces respectively with the predeterminedsystem clock on the data transfer line, then the frequency-modulateddigital data are sent out to the data transfer line respectively, thenthe digital data input via the data transfer line respectively aremultiplexed in synchronism with the predetermined system clock, and thenthe multiplexed digital data are transmitted to the external network.Meanwhile, when the multiplexed digital data transmitted from theexternal network are received by the plurality of external devices viathe data transfer line respectively, the multiplexed digital data aredistributed by inverse multiplexing in synchronism with thepredetermined system clock to send out to the data transfer line, thenthe digital data transmitted via the data transfer line respectively arereceived, then the frequency demodulation is executed to synchronize thedigital data which have been synchronized with the predetermined systemclock with the natural transmission speeds on the plurality ofinterfaces respectively, and then the digital data which are subjectedto the frequency demodulation are received by the plurality of externaldevices via the plurality of interfaces respectively.

Accordingly, like the above communication apparatus, the centralizationprocess of digital data can be executed by concentrating the digitaldata which being transmitted from the plurality of external deviceswhich can execute data exchange at their natural communication speeds orbeing transmitted from the external network, and also two-waycommunications between the external network and the plurality ofexternal devices can be carried out smoothly.

In the preferred embodiment of the present invention, the digital datainput via the data transfer line respectively are transformed intoplural packets and then transmitted to the external network on atime-division multiplex basis.

In the preferred embodiment of the present invention, the transmitterfurther comprises a plurality of information adding means for addingheader information including at least destination to the digital datawhich are divided into a predetermined proper unit with respect to theplurality of interfaces and then output.

According to this embodiment, the digital data can be firmly transmittedto the predetermined sender by referring to header information added bythe information adding means.

In the preferred embodiment of the present invention, the receiverfurther comprises a plurality of header information deleting means fordeleting header information from the digital data to which the headerinformation including at least destination are added and which are sentout from the distributor via the data transfer line.

According to this embodiment, the plurality of external devices canreceive raw data without including the extra information respectively bydeleting header information by the header information deleting means.

In the preferred embodiment of the present invention, the communicationapparatus further comprises a plurality of information adding means foradding header information including at least destination to the digitaldata which are divided into a predetermined proper unit with respect tothe plurality of interfaces and then output; and a plurality of headerinformation deleting means for deleting the header information from thedigital data to which the header information including at leastdestination are added and which are sent out from the distributor viathe data transfer line.

According to this embodiment, the digital data can be firmly transmittedto the predetermined sender by referring to header information added bythe information adding means, and the plurality of external devices canreceive raw data without including the extra information respectively bydeleting header information by the header information deleting means.

In the preferred embodiment of the present invention, data exchanges areexecuted between senders and destinations based on device referenceclocks peculiar to the plurality of external devices which aredistributed at predetermined distribution ratios of the predeterminedsystem clock.

According to this embodiment, since data exchange can be executedbetween the senders and the destinations based on the device referenceclocks peculiar to the plurality of external devices which aredistributed at the predetermined distribution ratios of thepredetermined system clock, smooth two-way communications can beimplemented between the external network and the plurality of externaldevices.

In order to achieve the above object, there is provided a transmittercomprising a data transfer line for transferring digital data; aplurality of interfaces connected to a plurality of external devices inone-by-one correspondence, and constructed so as to fit to transmissionspeeds peculiar to the plurality of external devices respectively; aplurality of frequency modulators connected to the plurality of externalinterfaces in one-by-one correspondence, for executing a frequencymodulation to synchronize the digital data which have naturaltransmission speeds on respective interfaces with a predetermined systemclock of multiplexer side, and then sending out the digital data whichare subjected to the frequency modulation to the data transfer linerespectively; a multiplexer for multiplexing the digital data which aretransmitted from the plurality of frequency modulators via the datatransfer line in synchronism with the predetermined system clock ofmultiplexer side, and then transmitting multiplexed digital data to anexternal network; and a clock generator for generating reference clocksincluding the predetermined system clock and then supplying thegenerated reference clocks to the plurality of frequency modulators andthe multiplexer respectively.

According to the present invention, first, in the plurality of frequencymodulators, the frequency modulation is executed to synchronize thedigital data which are output from the plurality of external deviceshaving their natural transmission speeds on the plurality of interfacesrespectively with the predetermined system clock of multiplexer side onthe data transfer line, then the frequency-modulated digital data aresent out to the data transfer line respectively. Then, the multiplexermultiplexes the digital data input via the data transfer linerespectively in synchronism with the predetermined system clock ofmultiplexer side, and then transmits the multiplexed digital data to theexternal network.

Accordingly, the centralization process of digital data can be executedby concentrating the digital data which being transmitted from theplurality of external devices which can execute data exchange at theirnatural communication speeds onto the multiplexer, and also the digitaldata multiplexed by the multiplexer can be transmitted to the externalnetwork.

In order to achieve the above object, there is provided a receivercomprising a data transfer line for transferring digital data; adistributor for receiving multiplexed digital data transmitted from anexternal network, and then distributing the multiplexed digital data byinverse multiplexing in synchronism with a predetermined system clock ofdistributor side in the data transfer line to send out to the datatransfer line; a plurality of interfaces connected to a plurality ofexternal devices in one-by-one correspondence, and constructed so as tofit to transmission speeds peculiar to the plurality of external devicesrespectively; a plurality of frequency demodulators for receiving thedigital data output from the distributor via the data transfer line,then executing a frequency demodulation to synchronize the digital datawhich have been synchronized with the predetermined system clock ofdistributor side with the natural transmission speeds on the pluralityof interfaces respectively, and then sending out the digital data whichare subjected to the frequency demodulation to the plurality ofinterfaces respectively; and a clock generator for generating referenceclocks including the predetermined system clock of distributor side, andthen supplying the reference clocks to the distributor and the pluralityof frequency demodulators respectively.

According to the present invention, the distributor receives themultiplexed digital data transmitted from the external network, and thendistributes the multiplexed digital data by inverse multiplexing insynchronism with the predetermined system clock on the data transferline to send out to the data transfer line. Then, the plurality offrequency demodulators execute the frequency demodulation to synchronizeinput digital data which have been synchronized with the predeterminedsystem clock of distributor side with the natural transmission speeds onthe plurality of interfaces respectively, and then sends out thefrequency-demodulated digital data to the plurality of interfacesrespectively. The digital data are then received by the plurality ofexternal devices via the plurality of interfaces respectively.

Accordingly, the centralization process of digital data can be executedby concentrating the multiplexed digital data which being transmittedfrom the external network onto the distributor, and also the digitaldata distributed by the distributor can be transformed into data formatshaving the communication speeds peculiar to the plurality of interfacesto enable reception by the external devices respectively.

In order to achieve the above object, there is provided a communicationapparatus comprising a data transfer line for transferring digital data;a distributor for receiving multiplexed data transmitted from anexternal network, and then distributing multiplexed digital data byinverse multiplexing in synchronism with a predetermined system clock ofdistributor side to send out to the data transfer line; a plurality ofinterfaces connected to a plurality of external devices in one-by-onecorrespondence, and constructed so as to fit to transmission speedspeculiar to the plurality of external devices respectively; a pluralityof frequency modulators connected to the plurality of interfaces inone-by-one correspondence, for executing a frequency modulation tosynchronize the digital data which have natural transmission speeds onrespective interfaces with a predetermined system clock of multiplexerside, and then sending out the digital data which are subjected to thefrequency modulation to the data transfer line respectively; a pluralityof frequency demodulators for receiving the digital data which areoutput from the distributor via the data transfer line, then executing afrequency demodulation to synchronize the digital data which have beensynchronized with the predetermined system clock of distributor sidewith the natural transmission speeds on the plurality of interfacesrespectively, and then sending out the digital data which are subjectedto the frequency demodulation to the plurality of interfacesrespectively; a multiplexer for multiplexing the digital data which aretransmitted from the plurality of frequency modulators via the datatransfer line in synchronism with the predetermined system clock ofmultiplexer side, and then transmitting multiplexed digital data to anexternal network; and a clock generator for generating reference clocksincluding the predetermined system clock of distributor side and thepredetermined system clock of multiplexer side, and then supplying thereference clocks to the distributor, the multiplexer, the plurality offrequency modulators, and the plurality of frequency demodulatorsrespectively.

According to the present invention, when the digital data transmittedfrom the plurality of external devices respectively are transmitted tothe external network via the data transfer line, in the plurality offrequency modulators, the frequency modulation is executed tosynchronize the digital data which have natural transmission speeds onrespective interfaces with the predetermined system clock on the datatransfer line, and then the frequency-modulated digital data are sentout to the data transfer line respectively. Then, the multiplexermultiplexes the digital data which are transmitted via the data transferline in synchronism with the predetermined system clock and thentransmits the multiplexed digital data to the external network.

Meanwhile, when the multiplexed digital data transmitted from theexternal network are received by the plurality of external devices viathe data transfer line respectively, in the distributor, the multiplexeddigital data transmitted from the external network are received, andthen the multiplexed digital data are distributed by inversemultiplexing in synchronism with the predetermined system clock on thedata transfer line to send out to the data transfer line. Then, theplurality of frequency demodulators receive the digital data output fromthe distributor via the data transfer line, then execute the frequencydemodulation to synchronize input digital data which have beensynchronized with the predetermined system clock on the data transferline with the natural transmission speeds on the plurality of interfacesrespectively, and then sending out the frequency-demodulated digitaldata to the plurality of interfaces respectively. The digital data arethen received by the plurality of external devices via the plurality ofinterfaces respectively.

Accordingly, the centralization process of digital data can be executedby concentrating the digital data, which being transmitted from theplurality of external devices which can execute data exchange at theirnatural communication speeds or being transmitted from the externalnetwork, onto the multiplexer or the distributor, and also the two-waycommunications between the external network and the plurality ofexternal devices can be carried out smoothly.

In order to achieve the above object, there is provided a communicationmethod for use in a communication system including, a data transfer linefor transferring digital data, and a plurality of interfaces connectedto a plurality of external devices in one-by-one correspondence, andconstructed so as to fit to transmission speeds peculiar to theplurality of external devices respectively, the communication methodcomprising the steps of: executing a frequency modulation to synchronizethe digital data which are output from the plurality of external deviceshaving the natural transmission speeds on the plurality of interfacesrespectively with a predetermined system clock of multiplexer side, andthen sending out the digital data which are subjected to the frequencymodulation to the data transfer line respectively; and multiplexing thedigital data which are input via the data transfer line respectively insynchronism with the predetermined system clock of multiplexer side, andthen transmitting multiplexed digital data to an external network;whereby the digital data which are transmitted from the plurality ofexternal devices respectively are sent to the external network via thedata transfer line, and receiving the multiplexed digital datatransmitted from the external network, and then distributing themultiplexed digital data by inverse multiplexing in synchronism with thepredetermined system clock of distributor side to send out to the datatransfer line; receiving the digital data transmitted via the datatransfer line respectively, and then executing a frequency demodulationto synchronize the digital data which have been synchronized with thepredetermined system clock of distributor side with the naturaltransmission speeds on the plurality of interfaces respectively; andreceiving the digital data which are subjected to the frequencydemodulation by the plurality of external devices via the plurality ofinterfaces respectively; whereby the multiplexed digital data which aretransmitted from the external network are received by the plurality ofexternal devices via the data transfer line respectively.

According to the present invention, when the digital data transmittedfrom the plurality of external devices respectively are transmitted tothe external network via the data transfer line, the frequencymodulation is executed to synchronize the digital data which are outputfrom the plurality of external devices having their natural transmissionspeeds on the plurality of interfaces respectively with thepredetermined system clock of multiplexer side, and then thefrequency-modulated digital data are sent out to the data transfer linerespectively. Then, the digital data which are transmitted via the datatransfer line respectively are multiplexed in synchronism with thepredetermined system clock of multiplexer side and then the multiplexeddigital data are transmitted to the external network. Meanwhile, whenthe multiplexed digital data transmitted from the external network arereceived by the plurality of external devices via the data transfer linerespectively, the multiplexed digital data transmitted from the externalnetwork are received, and then the multiplexed digital data aredistributed by inverse multiplexing in synchronism with thepredetermined system clock of distributor side to send out to the datatransfer line. Then, the frequency demodulation is executed tosynchronize input digital data which have been synchronized with thepredetermined system clock of distributor side with the transmissionspeeds peculiar to the plurality of interfaces respectively, and thenthe frequency-demodulated digital data are received by the plurality ofexternal devices via the plurality of interfaces respectively.

Accordingly, the centralization process of digital data can be executedby concentrating the digital data, which being transmitted from theplurality of external devices which can execute data exchange at theirnatural communication speeds or being transmitted from the externalnetwork, onto the multiplexing or distributing function portion, andalso the two-way communications between the external network and theplurality of external devices can be carried out smoothly.

In the preferred embodiment of the present invention, the digital datawhich are input via the data transfer line respectively are transformedinto plural packets and then transmitted to the external network on atime-division multiplex basis.

In the preferred embodiment of the present invention, data exchanges areexecuted between senders and destinations based on device referenceclocks peculiar to the plurality of external devices which aredistributed at predetermined distribution ratios of the predeterminedsystem clock.

According to this embodiment, since data exchange can be executedbetween the senders and the destinations based on the device referenceclocks peculiar to the plurality of external devices which aredistributed at the predetermined distribution ratios of thepredetermined system clock, smooth two-way communications can beimplemented between the external network and the plurality of externaldevices.

In the preferred embodiment of the present invention, the multiplexerside system clock and the distributor side system clock are set mutuallyat a common frequency.

In the preferred embodiment of the present invention, the transmitterfurther comprises a plurality of information adding means for addingheader information including at least destination to the digital datawhich are divided into a predetermined proper unit with respect to theplurality of interfaces and then output.

According to this embodiment, the digital data can be firmly transmittedto the predetermined sender by referring to header information added bythe information adding means.

In the preferred embodiment of the present invention, the receiverfurther comprises a plurality of header information deleting means fordeleting header information from the digital data to which the headerinformation including at least destination are added and which are sentout from the distributor via the data transfer line.

According to this embodiment, the plurality of external devices canreceive raw data without including the extra information respectively bydeleting header information by the header information deleting means.

In the preferred embodiment of the present invention, the communicationapparatus further comprises a plurality of information adding means foradding header information including at least destination to the digitaldata which are divided into a predetermined proper unit with respect tothe plurality of interfaces and then output; and a plurality of headerinformation deleting means for deleting the header information from thedigital data to which the header information including at least thedestination are added and which are sent out from the distributor viathe data transfer line.

According to this embodiment, the digital data can be firmly transmittedto the predetermined sender by referring to header information added bythe information adding means, and the plurality of external devices canreceive raw data without including the extra information respectively bydeleting header information by the header information deleting means.

In order to achieve the above object, there is provided a communicationmethod for use in a communication system including a data transfer linefor transferring digital data, and a plurality of interfaces connectedto a plurality of external devices in one-by-one correspondence, andconstructed so as to fit to transmission speeds peculiar to theplurality of external devices respectively, the communication methodcomprising the steps of: adding header information including at leastdestination to the digital data which have natural communication speedson the plurality of interfaces and are divided into a predeterminedproper unit of the plurality of interfaces and then output; executing afrequency modulation to synchronize the digital data to which the headerinformation are added with a predetermined system clock of multiplexerside, and then sending out the digital data which are subjected to thefrequency modulation to the data transfer line respectively; andmultiplexing the digital data which are input via the data transfer linerespectively in synchronism with the predetermined system clock ofmultiplexer side, and then transmitting multiplexed digital data to anexternal network; whereby the digital data which are transmitted fromthe plurality of external devices respectively are sent to the externalnetwork via the data transfer line, and receiving the multiplexeddigital data transmitted from the external network, and thendistributing the multiplexed digital data by inverse multiplexing insynchronism with a predetermined system clock of distributor side tosend out to the data transfer line; receiving the digital data which aretransmitted via the data transfer line respectively, and then executinga frequency demodulation to synchronize the digital data which have beensynchronized with the predetermined system clock of distributor sidewith the natural transmission speeds on the plurality of interfacesrespectively; and receiving the digital data which are subjected to thefrequency demodulation by the plurality of external devices via theplurality of interfaces respectively; whereby the multiplexed digitaldata which are transmitted from the external network are received by theplurality of external devices via the data transfer line respectively.

According to the present invention, when the digital data transmittedfrom the plurality of external devices respectively are transmitted tothe external network via the data transfer line, header informationincluding at least destination are added respectively to the digitaldata which have their natural communication speeds on the plurality ofinterfaces and are divided into predetermined proper units on theplurality of interfaces respectively and then output, then the frequencymodulation is executed to synchronize the digital data to which theheader information are added respectively with the predetermined systemclock of multiplexer side, and then the frequency-modulated digital dataare sent out to the data transfer line respectively. Then, the digitaldata which are transmitted via the data transfer line respectively aremultiplexed in synchronism with the predetermined system clock ofmultiplexer side and then the multiplexed digital data are transmittedto the external network.

In order to achieve the above object, there is provided a communicationmethod for use in a communication system including a data transfer linefor transferring digital data, and a plurality of interfaces connectedto a plurality of external devices in one-by-one correspondence, andconstructed so as to fit to transmission speeds peculiar to theplurality of external devices respectively, the communication methodcomprising the steps of: executing a frequency modulation to synchronizethe digital data which have natural communication speeds on theplurality of interfaces with a predetermined system clock of multiplexerside; adding header information including at least destination to thedigital data which are subjected to the frequency modulation and aredivided into a predetermined proper unit of the plurality of interfacesand then output respectively, and then sending out the digital data towhich the header information are added to the data transfer linerespectively; and multiplexing the digital data which are input via thedata transfer line respectively in synchronism with the predeterminedsystem clock of multiplexer side, and then transmitting multiplexeddigital data to an external network; whereby the digital data which aretransmitted from the plurality of external devices respectively are sentto the external network via the data transfer line, and receiving themultiplexed digital data transmitted from the external network, and thendistributing the multiplexed digital data by inverse multiplexing insynchronism with a predetermined system clock of distributor side tosend out to the data transfer line; receiving the digital data which aretransmitted via the data transfer line respectively, and then executinga frequency demodulation to synchronize the digital data which have beensynchronized with the predetermined system clock of distributor sidewith the natural transmission speeds on the plurality of interfacesrespectively; and receiving the digital data which are subjected to thefrequency demodulation by the plurality of external devices via theplurality of interfaces respectively; whereby the multiplexed digitaldata which are transmitted from the external network are received by theplurality of external devices via the data transfer line respectively.

According to the present invention, when the digital data transmittedfrom the plurality of external devices respectively are transmitted tothe external network via the data transfer line, the frequencymodulation is executed to synchronize the digital data which have theirnatural transmission speeds on the plurality of interfaces respectivelywith the predetermined system clock of multiplexer side, then the headerinformation including at least destination are added respectively to thedigital data which have been subjected to the frequency modulation anddivided into predetermined proper units on the plurality of interfacesand then output respectively, and then the digital data to which theheader information are added are sent out to the data transfer linerespectively. Then, the digital data which are received via the datatransfer line respectively are multiplexed in synchronism with thepredetermined system clock of multiplexer side and then the multiplexeddigital data are transmitted to the external network.

In order to achieve the above object, there is provided, in acommunication system constructed by connecting a plurality ofcommunication apparatuses via a data transmission line to execute dataexchange between any communication apparatuses, the plurality ofcommunication apparatuses are constructed so as to access the datatransmission line at timing periods peculiar to respective communicationapparatuses in synchronism with a common system clock among respectivecommunication apparatuses, and the timing periods peculiar to respectivecommunication apparatuses are set to be shifted mutually such thataccesses to the data transmission line are not simultaneously generatedfrom the plurality of communication apparatuses.

According to the present invention, the plurality of communicationapparatuses are constructed so as to access the data transmission lineat their timing periods peculiar to respective communication apparatusesin synchronism with the common system clock among the plurality ofcommunication apparatuses and also the timing periods peculiar torespective communication apparatuses are set to be shifted mutually suchthat access to the data transmission line are not simultaneouslygenerated from the plurality of communication apparatuses. Therefore,the plurality of communication apparatuses can access the datatransmission line in parallel respectively with avoiding collision ofdata. As a result, smooth two-way communications between anycommunication apparatuses can be realized while assuring excellentreal-time facility.

In order to achieve the above object, there is provided, in acommunication system constructed by connecting a plurality ofcommunication apparatuses via a star configuration data transmissionline which is arranged around one centralized controller to execute dataexchange between any communication apparatuses, the plurality ofcommunication apparatuses are constructed so as to access thecentralized controller at timing periods peculiar to respectivecommunication apparatuses in synchronism with a common system clockamong respective communication apparatuses, and the timing periodspeculiar to the communication apparatuses are set to be shifted mutuallysuch that accesses to the centralized controller are not simultaneouslygenerated from the plurality of communication apparatuses.

According to the present invention, the plurality of communicationapparatuses are constructed so as to access the centralized controllerat their timing periods peculiar to respective communication apparatusesin synchronism with the common system clock among the plurality ofcommunication apparatuses and in addition the timing periods peculiar torespective communication apparatuses are set to be shifted mutually suchthat access to the centralized controller are not simultaneouslygenerated from the plurality of communication apparatuses. Hence, theplurality of communication apparatuses can access the centralizedcontroller in parallel respectively with avoiding collision of data. Asa result, smooth two-way communications between any communicationapparatuses and the centralized controller can be realized whileassuring excellent real-time facility and in addition the communicationsystem having a simple configuration to which the centralized controllerand the buffer memory for storing overflow data temporarily are notrequired can be achieved.

In order to achieve the above object, there is provided, in acommunication method for use in a communication system which isconstructed by connecting a plurality of communication apparatuses via adata transmission line to execute data exchange between anycommunication apparatuses, the plurality of communication apparatusesare constructed so as to access the data transmission line insynchronism with predetermined timing clocks which are set to respectivecommunication apparatuses in synchronism with a common system clockamong respective communication apparatuses, when data exchange isexecuted between a sender communication apparatus and a destinationcommunication apparatus among the plurality of communicationapparatuses, communication channels can be established by producing thepredetermined timing clocks which are commonly used between the sendercommunication apparatus and the destination communication apparatus, thesender communication apparatus can execute data transmission insynchronism with the predetermined timing clock, and the destinationcommunication apparatus can receive data in synchronism with thepredetermined timing clock.

According to the present invention, when data exchange is to be executedbetween the sender communication apparatus and the destinationcommunication apparatus, first of all, a communication route isgenerated by establishing a predetermined timing clock used commonlybetween both communication apparatuses, then the sender communicationapparatus executes data transmission in synchronism with a predeterminedtiming clock while the destination communication apparatus executes datareception in synchronism with the predetermined timing clock.Accordingly, the plurality of communication apparatuses can access thedata transmission lines in parallel respectively with avoiding collisionof data. As a result, smooth two-way communications between anycommunication apparatuses can be realized while assuring excellentreal-time facility.

In order to achieve the above object, there is provided, in acommunication method for use in a communication system which isconstructed by connecting a plurality of communication apparatuses, towhich one external device or two or more external devices are connectedrespectively, via a data transmission line to execute data exchangebetween any external devices, between any communication apparatuses, orbetween any external device and any communication apparatus, at leastone of communication apparatuses out of the plurality of communicationapparatuses can generate clock allocation information in connection withdistribution ratios of a common system clock among the plurality ofcommunication apparatuses to various external devices respectively basedon all device connection information including type of the externaldevices connected to the plurality of communication apparatusesconstituting the communication system, and can transmit the clockallocation information to overall communication apparatuses includingits own communication apparatus, the plurality of communicationapparatuses including the at least of communication apparatus executedata can exchange between any sender and any destination based on devicereference clocks peculiar to various external devices and distributed atdistribution ratios of the system clock according to the clockallocation information, and a plurality of device reference clockspeculiar to the various external devices are set such that respectiverising times of their pulses are shifted mutually with regard to a factthat pulse rising timings as data communication timings of the variousexternal devices are not generated simultaneously between the externaldevices.

According to the present invention, at least one of the communicationapparatuses out of the plurality of communication apparatuses generatesthe clock allocation information concerning the distribution ratios ofthe system clock common to the plurality of communication apparatusesfor respective external devices based on the all device connectioninformation, and transmits the generated clock allocation information toall communication apparatuses including own communication apparatus. Inresponse to the clock allocation information, the plurality ofcommunication apparatuses including own communication apparatus executedata exchange between any sender and any destination based on the devicereference clocks which are distributed at distribution ratios of thesystem clock in compliance with the clock allocation information andpeculiar to various external devices.

In this manner, communication data transmitted from various externaldevices are transmitted to the data transmission line respectively insynchronism with the communication timings in compliance with the devicereference clocks peculiar to respective external devices and also pulserising timings which serve as the communication timings for thecommunication data being transmitted from various external devicesrespectively are set to be shifted mutually. Therefore, pluralcommunication data can be prevented beforehand from being transmittedsimultaneously from different senders and thus collision of thecommunication data can be avoided firmly. As a result, the communicationapparatus which is able to improve communication efficiency remarkablycan be realized.

In order to achieve the above object, there is provided, in acommunication method for use in a communication system which isconstructed by connecting a plurality of communication apparatuses, towhich one external device or two or more external devices are connectedrespectively, via a data transmission line to execute data exchangebetween any external devices, between any communication apparatuses, orbetween any external device and any communication apparatus, at leastone of communication apparatuses out of the plurality of communicationapparatuses can generate clock allocation information assigned tovarious external devices respectively in connection with distributionratios of a common system clock among the plurality of communicationapparatuses based on all device connection information including type ofthe external devices which are connected to the plurality ofcommunication apparatuses constituting the communication system, and cantransmit the clock allocation information to overall communicationapparatuses, including its own communication apparatus, the plurality ofcommunication apparatuses including the at least of communicationapparatus execute data can exchange between any sender and anydestination based on device reference clocks peculiar to variousexternal devices and distributed at distribution ratios of the systemclock according to the clock allocation information, and a plurality ofdevice reference clocks peculiar to the various external devices are setsuch that respective trailing times of their pulses are shifted mutuallywith regard to a fact that pulse trailing timings as data communicationtimings of the various external devices are not generated simultaneouslybetween the external devices.

According to the present invention, at least one of the communicationapparatuses out of the plurality of communication apparatuses generatesthe clock allocation information concerning the distribution ratios ofthe system clock common to the plurality of communication apparatusesfor respective external devices based on the all device connectioninformation, and transmits the generated clock allocation information toall communication apparatuses including own communication apparatus. Inresponse to the clock allocation information, the plurality ofcommunication apparatuses including own communication apparatus executedata exchange between any sender and any destination based on the devicereference clocks which are distributed at distribution ratios of thesystem clock in compliance with the clock allocation information andpeculiar to various external devices.

Like this, communication data transmitted from various external devicesare transmitted to the data transmission line respectively insynchronism with the communication timings in compliance with the devicereference clocks peculiar to respective external devices and also pulserising timings which serve as the communication timings for thecommunication data being transmitted from various external devicesrespectively are set to be shifted mutually. Therefore, pluralcommunication data can be prevented beforehand from being transmittedsimultaneously from different senders and thus collision of thecommunication data can be avoided firmly. As a result, the communicationapparatus which is able to improve communication efficiency remarkablycan be realized.

In order to achieve the above object, there is provided, in acommunication system which is constructed by connecting a plurality ofcommunication apparatuses, to which one external device or two or moreexternal devices are connected respectively, via a data transmissionline to execute data exchange between any external devices, between anycommunication apparatuses, or between any external device and anycommunication apparatus, at least one of communication apparatuses outof the plurality of communication apparatuses comprising: an all deviceconnection information storing means for storing all device connectioninformation including type of the external devices which are connectedrespectively to the plurality of communication apparatuses constitutingthe communication system; a clock allocating means for generating clockallocation information concerning distribution ratios of a system clockwhich is common among the plurality of communication apparatuses forrespective external devices, based on the all device connectioninformation stored in the all device connection information storingmeans; and a clock allocation information transmitting means fortransmitting the clock allocation information generated by the clockallocating means to all communication apparatuses including owncommunication apparatus; and the plurality of communication apparatusesincluding the at least one of communication apparatus comprising: aclock allocation information receiving means for receiving the clockallocation information transmitted from the clock allocation informationtransmitting means; and a data exchange controlling means forcontrolling data exchange between any sender and any destination, basedon device reference clocks peculiar to respective external devices whichare distributed at the distribution ratios of the system clock accordingto the clock allocation information received by the clock allocationinformation receiving means; wherein the plurality of device referenceclocks peculiar to the various external devices respectively are setsuch that respective rising times of their pulses are shifted mutuallywith regard to a fact that pulse rising timings as data communicationtimings of the various external devices are not simultaneously generatedmutually between the external devices.

According to the present invention, in at least one of communicationapparatuses out of the plurality of communication apparatuses, the clockallocating means generates clock allocation information concerningdistribution ratios of the system clock which is common among theplurality of communication apparatuses for respective external devices,based on all device connection information stored in all deviceconnection information storing means, and the clock allocationinformation transmitting means transmits the clock allocationinformation generated by the clock allocating means to all communicationapparatuses including own communication apparatus.

On the contrary, in the plurality of communication apparatuses includingat least one of communication apparatuses, the clock allocationinformation receiving means receives the clock allocation informationtransmitted from the clock allocation information transmitting means,and the data exchange controlling means controls data exchange betweenany sender and any destination, based on device reference clocks whichare peculiar to respective external devices and are distributed at thedistribution ratios of the system clock according to the clockallocation information received by the clock allocation informationreceiving means.

In this fashion, communication data transmitted from various externaldevices are transmitted to the data transmission line respectively insynchronism with the communication timings in compliance with the devicereference clocks peculiar to respective external devices and also pulserising timings which serve as the communication timings for thecommunication data being transmitted from various external devicesrespectively are set to be shifted mutually. Therefore, pluralcommunication data can be prevented beforehand from being transmittedsimultaneously from different senders and thus collision of thecommunication data can be avoided firmly. As a result, the communicationapparatus which is able to improve communication efficiency remarkablycan be realized.

In the preferred embodiment of the present invention, the plurality ofdevice reference clocks peculiar to the various external devices includea command dedicated clock for transmitting a command.

According to this embodiment, since the plurality of device referenceclocks peculiar to various external devices are constructed to includethe command dedicated clock for command transmission, the communicationsystem which is able to transmit the command from the sender to thedestination with a simple configuration can be implemented.

In order to achieve the above object, there is provided, in acommunication system which is constructed by connecting a plurality ofcommunication apparatuses, to which one external device or two or moreexternal devices are connected respectively, via a data transmissionline to execute data exchange between any external devices, between anycommunication apparatuses, or between any external device and anycommunication apparatus, at least one of communication apparatuses outof the plurality of communication apparatuses comprising: an all deviceconnection information storing means for storing all device connectioninformation including type of the external devices which are connectedrespectively to the plurality of communication apparatuses constitutingthe communication system; a clock allocating means for generating clockallocation information concerning distribution ratios of a system clockwhich is common among the plurality of communication apparatuses forrespective external devices, based on the all device connectioninformation stored in the all device connection information storingmeans; and a clock allocation information transmitting means fortransmitting the clock allocation information generated by the clockallocating means to all communication apparatuses including owncommunication apparatus; and the plurality of communication apparatusesincluding the at least one of communication apparatus comprising: aclock allocation information receiving means for receiving the clockallocation information transmitted from the clock allocation informationtransmitting means; and a data exchange controlling means forcontrolling data exchange between any sender and any destination, basedon device reference clocks peculiar to respective external devices whichare distributed at the distribution ratios of the system clock accordingto the clock allocation information received by the clock allocationinformation receiving means; wherein the plurality of device referenceclocks peculiar to the various external devices respectively are setsuch that respective trailing times of their pulses are shifted mutuallywith regard to a fact that pulse trailing timings as data communicationtimings of the various external devices are not simultaneously generatedmutually between the external devices.

According to the present invention, in at least one of communicationapparatuses out of the plurality of communication apparatuses, the clockallocating means generates clock allocation information concerningdistribution ratios of the system clock which is common among theplurality of communication apparatuses for respective external devices,based on all device connection information stored in all deviceconnection information storing means, and the clock allocationinformation transmitting means, transmits the clock allocationinformation generated by the clock allocating means to all communicationapparatuses including own communication apparatus.

While, in the plurality of communication apparatuses including at leastone of communication apparatuses, the clock allocation informationreceiving means receives the clock allocation information transmittedfrom the clock allocation information transmitting means, and the dataexchange controlling means controls data exchange between any sender andany destination, based on device reference clocks which are peculiar torespective external devices and are distributed at the distributionratios of the system clock according to the clock allocation informationreceived by the clock allocation information receiving means.

In this manner, communication data transmitted from various externaldevices are transmitted to the data transmission line respectively insynchronism with the communication timings in compliance with the devicereference clocks peculiar to respective external devices and also pulserising timings which serve as the communication timings for thecommunication data being transmitted from various external devicesrespectively are set to be shifted mutually. Therefore, pluralcommunication data can be prevented beforehand from being transmittedsimultaneously from different senders and thus collision of thecommunication data can be avoided firmly. As a result, the communicationapparatus which is able to improve communication efficiency remarkablycan be realized.

In the preferred embodiment of the present invention, the plurality ofdevice reference clocks peculiar to the various external devices includea command dedicated clock for transmitting a command.

According to this embodiment, since the plurality of device referenceclocks peculiar to various external devices are constructed to includethe command dedicated clock for command transmission, the communicationsystem which is able to transmit the command from the sender to thedestination with a simple configuration can be implemented.

The nature, principle and utility of the invention will become moreapparent from the following detailed description when read inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings:

FIG. 1 is a block circuit diagram showing a configuration of a firstcommunication apparatus according to a first embodiment of the presentinvention;

FIG. 2 is a block circuit diagram showing a configuration of a firsttransmitter according to the first embodiment of the present invention;

FIG. 3 is a block circuit diagram showing a configuration of a firstreceiver according to the first embodiment of the present invention;

FIG. 4 is a timing chart illustrating an operation of the firstcommunication apparatus according to the first embodiment of the presentinvention;

FIGS. 5A and 5B are views showing data formats used in the firstcommunication apparatus according to the first embodiment of the presentinvention;

FIG. 6 is a block circuit diagram showing a configuration of a secondcommunication apparatus according to a second embodiment of the presentinvention;

FIG. 7 is a block circuit diagram showing a configuration of a secondtransmitter according to the second embodiment of the present invention;

FIG. 8 is a block circuit diagram showing a configuration of a secondreceiver according to the second embodiment of the present invention;

FIGS. 9A and 9B are views showing data formats used in the secondcommunication apparatus according to the second embodiment of thepresent invention respectively;

FIGS. 10A and 10B are views showing another data formats used in thesecond communication apparatus according to the second embodiment of thepresent invention respectively;

FIGS. 11A and 11B are views showing still another data formats used inthe second communication apparatus according to the second embodiment ofthe present invention respectively;

FIG. 12 is a block circuit diagram showing a configuration of a thirdcommunication apparatus according to a third embodiment of the presentinvention, which is a modification of the communication apparatusaccording to the first embodiment of the present invention;

FIG. 13 is a block circuit diagram showing a configuration of a fourthcommunication apparatus according to a fourth embodiment of the presentinvention, which is a modification of the communication apparatusaccording to the second embodiment of the present invention;

FIG. 14 is a schematic block diagram showing a first communicationsystem according to a fifth embodiment of the present invention;

FIG. 15 is a schematic block diagram showing a second communicationsystem according to a sixth embodiment of the present invention;

FIG. 16 is a schematic block diagram showing a third communicationsystem according to a seventh embodiment of the present invention;

FIG. 17 is a schematic block diagram showing a fourth communicationsystem according to an eighth embodiment of the present invention;

FIG. 18 is a block circuit diagram showing a configuration of a fifthcommunication apparatus according to a ninth embodiment of the presentinvention, which is another modification of the first communicationapparatus according to the first embodiment of the present Invention;

FIG. 19 is a block circuit diagram showing a configuration of a sixthcommunication apparatus according to a tenth embodiment of the presentinvention, which is another modification of the second communicationapparatus according to the second embodiment of the present invention;

FIG. 20 is a table showing an example of device connection informationreferred to in the fourth communication system according to the eighthembodiment of the present invention and the fifth and sixthcommunication apparatuses according to ninth and tenth embodiments ofthe present invention;

FIGS. 21A to 21K are timing charts illustrating examples of devicereference clocks allocated respectively to various external devices inthe fifth and sixth communication apparatuses according to the ninth andtenth embodiments of the present invention; and

FIG. 22 is a clock allocation table showing clock allocation states to aplurality of external devices in the fifth and sixth communicationapparatuses according to the ninth and tenth embodiments of the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

Transmitters, receivers, communication apparatuses, communicationmethods, and communication systems according to plural embodiments ofthe present invention will be explained with reference to accompanyingdrawings hereinafter.

Various vehicle-equipped external devices will be illustrated as one ormore than two external devices which are connected to a communicationapparatus of the present invention respectively, and a vehicle networkwhich is constructed by connecting various vehicle-equipped devices soas to enable data exchange therebetween will be illustrated as anexternal network connected to the communication apparatus. Where theexternal network signifies a network, for example, which is constructedby connecting the communication apparatuses, to which one or more thantwo external devices are connected respectively, via a data transmissionline, like a communication system according to the present invention.

First, as shown in FIGS. 1 to 3, a first communication apparatus 1according to a first embodiment of the present invention is constructedto include a first transmitter 2 and a first receiver 4. Thecommunication apparatus 1 has a function of implementing acentralization process by which various data, etc. are collected on acommon data transfer line. More particularly, the centralization processcan be achieved by multiplexing digital data which are transmitted froma plurality of external devices via the common data transfer linerespectively, then transmitting multiplexed digital data to an externalnetwork installed in the vehicle, for example, and then distributing themultiplexed digital data received from the external network by inversemultiplexing and then receiving distributed digital data by a concernedexternal device via the common data transfer line respectively, wherebythe digital data having their natural communication speeds specifiedbased on a plurality of protocols can be communicated via the commondata transfer line. The plurality of external devices are composed of apersonal computer (PC), a telephone (TEL), etc., for example, andexecute data exchange at their natural communication speeds which arespecified based on mutually different protocols respectively. As a datatransmission system upon connecting the communication apparatus of thepresent invention to the external network, for example, all kinds ofdata transmission systems, for example, a radio communication such as anoptical communication using a laser beam, a wire communication using anoptical fiber cable or a conductor cable, etc. may be employed.

In more detail, the first communication apparatus 1 according to thefirst embodiment of the present invention comprises a data transfer line(BUS) 3, a distributor or demultiplexer (DMUX) 7, a multiplexer (MUX)11, various interfaces 19, 27, 35, 43, 51, 59, frequency modulators (FM)15, 23, 31, 39, 47, 55, frequency demodulators (FDM) 17, 25, 33, 41, 49,57, and a clock generator (PLL/CG; Phase Lock Loop/Clock Generator) 9.In addition, a personal computer (PC) 21, a mobile telephone (TEL) 29, aDVD-ROM drive 37, a digital TV set 45, a music CD player (CD) 53, aspeed sensor 61, all being installed on the vehicle, for example, areconnected to the communication apparatus 1. More specifically, the datatransfer line (BUS) 3 made of a bus type line, for example, transmitsdigital data including data such as sound or video data, synchronizingsignals, sender and destination information which are transmitted from aplurality of external devices to execute data exchange at theircommunication speeds specified based on mutually different protocols, ortransmitted from the external network. The distributor (DMUX) 7 receivesmultiplexed digital data via a network receiver 5 which receives themultiplexed digital data transmitted from the external network, anddistributes the multiplexed digital data by inverse multiplexing to sendout to the data transfer line 3. The multiplexer (MUX) 11 multiplexesthe digital data transmitted from a plurality of external devices viathe data transfer line 3, and transmits the multiplexed digital data tothe external network via a network transmitter 13. Various interfaces19, 27, 35, 43, 51, 59 are connected to a plurality of external devices21, 29, 37, 45, 53, 61 in one-by-one correspondence and are normalizedso as to fit to respective protocols used for the external devices, andincludes an IEEE1394 interface 19, a USB (Universal Serial Bus)interface 27, an ATAPI (AT Attachment Packet Interface) interface 35, aPES (Packetized Elementary Stream) interface 43, a 958M interface 51which is standardized by SPDIF (CIE/IEC 958) which has been invented bythe inventor of the present invention and has already been filed, andenables communication of both standard speed data and n time speed dataof a music CD player, and a SCI (Serial Command Interface) interface 59which is used to communicate command data, etc. The frequency modulators(FM) 15, 23, 31, 39, 47, 55 which are connected to these interfaces 19,27, 35, 43, 51, 59 in one-by-one correspondence, execute frequencymodulation to synchronize output data having their natural communicationspeeds on respective interfaces with a high frequency of a system clockSYCLK such as 100 MHz on the data transfer line 3, and send out thedigital data which are subjected to the frequency modulation to the datatransfer line 3. The frequency demodulators (FDM) 17, 25, 33, 41, 49, 57receive digital data transmitted from the distributor (DMUX) 7 via thedata transfer line 3, execute frequency demodulation to synchronize thedigital data which have been synchronized with the frequency of thesystem clock SYCLK on the data transfer line 3 with the naturalcommunication speeds on respective interfaces, and send out the digitaldata which have been subjected to the frequency demodulation torespective interfaces. The clock generator (PLL/CG) 9 generatesreference clocks having respective frequencies such as a system clockSYCLK on the data transfer line 3, a synchronizing signal LRCK forinputting/outputting digital audio data on the 958M interface 51, aclock synchronizing signal BSSYC for packet communication on theIEEE1394 interface 19, the USB interface 27, the ATAPI interface 35, andthe PES interface 43, an enable signal RE on the interfaces 19, 27, 35,43, etc., as shown in FIG. 4, and has a phase lock loop (PLL) functionto maintain phases of these reference clocks at high precision, and thensupplies the reference clocks to the distributor (DMUX) 7, themultiplexer (MUX) 11, the frequency modulator (FM) 15, 23, 31, 39, 47,55 and the frequency demodulators (FDM) 17, 25, 33, 41, 49, 57respectively.

In order to set the frequency of the system clock SYCLK on the datatransfer line 3, it is preferable that such frequency may be set to haveintegral ratios against operation frequencies of respective interfaces,for example, so as to enable easy establishment of synchronizationbetween the frequency of the system clock SYCLK and the operationfrequencies while referring to clock frequencies which correspond to thecommunication speeds peculiar to respective interfaces 19, 27, 35, 43,51, 59, bit lengths occupied by header information which includesynchronizing signals described later, sender and destination, etc.appropriately, and the like.

Next, the first transmitter 2 to which the personal computer (PC) 21 andthe mobile telephone (TEL) 29 are connected as external devicesaccording to the first embodiment of the present invention will beexplained as an example with reference to FIG. 2 hereunder.

As shown in FIG. 2, the first transmitter 2 according to the firstembodiment of the present invention comprises the IEEE1394 interface 19and the USB interface 27 which are connected the personal computer (PC)21 and the mobile telephone (TEL) 29 as the external devices inone-by-one correspondence; the frequency modulators (FM) 15, 23 whichexecute frequency modulation to synchronize output data from theinterfaces 19, 27 with the frequency of a system clock SYCLK on the datatransfer line 3, and send out the digital data which are subjected tothe frequency modulation to the data transfer line 3; the multiplexer(MUX) 11 which multiplexes the digital data transmitted from theexternal devices 21, 29 via the data transfer line 3, and transmits themultiplexed digital data to the external network via a networktransmitter 13; and the clock generator (PLL/CG) 9 (not shown in FIG. 2)which generates various reference clocks having their own naturalfrequencies such as the system clock SYCLK which is an operationreference clock of the transmitter 2, a clock synchronizing signal BSSYCon the IEEE1394 interface 19 or the USB interface 27, and the enablesignal RE on the interfaces 19, 27, etc., and has a phase lock loop(PLL) function to maintain phases of these reference clocks at highprecision, and then supplies the reference clocks to the frequencymodulator (FM) 15, 23 and the multiplexer (MUX) 11 respectively.

Although the first transmitter 2 according to the first embodiment ofthe present invention has been explained while taking the case where thepersonal computer (PC) 21 and the mobile telephone (TEL) 29 areconnected as the external devices, the present invention is not limitedto this situation. One or more than two any external devices whichexecute data exchange at their communication speeds specified accordingto various protocols may be connected in place of the above two systemexternal devices.

Then, the first receiver 4 according to the first embodiment of thepresent invention will be explained with reference to FIG. 3 whiletaking the case where the personal computer (PC) 21 and the mobiletelephone (TEL) 29 are connected as the external devices, like thetransmitter 2.

As shown in FIG. 3, the first receiver according to the first embodimentof the present invention comprises the distributor (DMUX) 7 whichreceives multiplexed digital data via a network receiver 5 whichreceives the multiplexed digital data transmitted from the externalnetwork, and distributes the multiplexed digital data by inversemultiplexing to send out to the data transfer line 3; the frequencydemodulators (FDM) 17, 25 which receive digital data transmitted fromthe distributor (DMUX) 7 via the data transfer line 3, execute frequencydemodulation to synchronize the digital data which have beensynchronized with the system clock SYCLK on the data transfer line 3with the natural communication speeds on respective interfaces 19, 27,and send out the digital data which have been subjected to the frequencydemodulation to respective interfaces 19, 27; the IEEE1394 interface 19and the USB interface 27 which are connected to the personal computer(PC) 21 and the mobile telephone (TEL) 29 as the external devices inone-by-one correspondence; and the clock generator (PLL/CG) 9 (not shownin FIG. 3) which generates various reference clocks having their ownnatural frequencies such as the system clock SYCLK which is an operationreference clock of the receiver 4, the clock synchronizing signal BSSYCfor packet communication on the IEEE1394 interface 19 and the USBinterface 27, an enable signal RE on the interfaces 19, 27, and has thephase lock loop (PLL) function to maintain phases of these referenceclocks at high precision, and then supplies the reference clocks to thedistributor (DMUX) 7 and the frequency demodulators (FDM) 17, 25respectively.

The first receiver 4 according to the first embodiment of the presentinvention has been explained while taking the case where the personalcomputer (PC) 21 and the mobile telephone (TEL) 29 are connected as theexternal devices, but the present invention is not limited to thissituation. One or more than two any external devices which execute dataexchange at their communication speeds specified according to variousprotocols may be connected in place of the above two system externaldevices.

Next, operations of the first transmitter 2, the first receiver 4, andthe first communication apparatus 1 constructed as above according tothe first embodiment of the present invention will be explainedhereunder. Since operations of the transmitter 2 and the receiver 4 areincluded in the operation of the communication apparatus 1, theirexplanations are omitted hereunder.

With the first communication apparatus 1 according to the firstembodiment of the present invention, in order to transmit the digitaldata transmitted from a plurality of external devices 21, 29, 37, 45,53, 61 respectively to the external network via the data transfer line3, first of all, the frequency modulation is executed by a plurality offrequency modulators (FM) 15, 23, 31, 39, 47, 55 so as to synchronizethe digital data output from a plurality of external devices 21, 29, 37,45, 53, 61 having their natural communication speeds on a plurality ofinterfaces 19, 27, 35, 43, 51, 59 respectively with the frequency of thepredetermined system clock SYCLK supplied from the clock generator(PLL/CG) 9 on the data transfer line 3. The digital data which aresubjected to the frequency modulation are then sent out to the datatransfer line 3 respectively.

In other words, as shown in FIG. 4, in the case that a first referenceclock frequency which corresponds to the communication speed on theinterface connected to a certain external device is a frequency obtainedby 1/3 frequency-dividing the predetermined system clock SYCLK on thedata transfer line 3, for example, timings of the first reference clockare set such that one rising pulse of the first reference clock isgenerated during when three rising pulses of the system clock SYCLK aregenerated for three pulse periods. The digital data output from thecertain external device are output to the data transfer line 3 insynchronism with the generation timing of this one rising pulse.

As shown in FIG. 4, as for the first reference clock which correspondsto the communication speed on the interface connected to the certainexternal device and a second reference clock which corresponds to thecommunication speed on the interface connected to the external devicehaving the protocol different from that of the above external device,their pulse rising timings are set respectively while taking account ofthe event that rising timings of both pulses do not occursimultaneously. This principle can be similarly applied between aplurality of reference clocks which correspond to the communicationspeeds on respective interfaces if three or more external devices areconnected via the data transfer line 3, for example.

When received the digital data which are subjected to the abovefrequency modulation, the multiplexer (MUX) 11 multiplexes the digitaldata which are input via the data transfer line 3 respectively insynchronism with the system clock SYCLK, and then transmits multiplexeddigital data to the external network.

Meanwhile, in order to receive the multiplexed digital data transmittedfrom the external network by a plurality of external devices 21, 29, 37,45, 53, 61 via the data transfer line 3, at first the distributor (DMUX)7 receives the multiplexed digital data being transmitted from theexternal network, and then distributes the multiplexed digital data byinverse multiplexing in synchronism with the system clock SYCLK to sendout to the data transfer line 3. Next, a plurality of frequencydemodulators (FDM) 17, 25, 33, 41, 49, 57 receive the digital data sentout from the distributor (DMUX) 7 via the data transfer line 3, thenexecutes the frequency demodulation to synchronize the received digitaldata which have been synchronized with the frequency of thepredetermined system clock SYCLK supplied from the clock generator(PLL/CG) 9 on the data transfer line 3 with the natural communicationspeeds on the plurality of interfaces 19, 27, 35, 43, 51, 59, and thensend out the digital data which have been subjected to the frequencydemodulation to the plurality of interfaces 19, 27, 35, 43, 51, 59respectively. These digital data are then received by the plurality ofexternal devices 21, 29, 37, 45, 53, 61 via the plurality of interfaces19, 27, 35, 43, 51, 59 respectively.

Therefore, according to the first communication apparatus 1 of the firstembodiment of the present invention, a centralization process of digitaldata can be executed by concentrating the digital data, which beingtransmitted from a plurality of external devices 21, 29, 37, 45, 53, 61which can execute data exchange at their natural transmission speedsspecified according to mutually different protocols respectively orbeing transmitted from the external network, onto the common datatransfer line 3, a common multiplexer, or a common distributor, and alsosmooth two-way communications between the external network and theplurality of external devices 21, 29, 37, 45, 53, 61 can be implemented.

Further, according to the first communication apparatus 1 of the firstembodiment of the present invention, since the digital data beingmultiplexed based on a time-division multiplex system on the common datatransfer line 3, for example, are transmitted in synchronism with thepredetermined system clock on the data transfer line 3, any externaldevice out of the plurality of external devices can access readily suchdigital data. Hence, as will be described later, according to a thirdcommunication apparatus 200 of the third embodiment shown in FIG. 12,smooth two-way communications can be implemented easily between aplurality of external devices other than the above two-waycommunications between the external network and the plurality ofexternal devices.

The operation of the above first communication apparatus 1 will beexplained in more detail. In the plurality of frequency modulators (FM)15, 23, 31, 39, 47, 55, the frequency modulation is executed tosynchronize digital data (DATA) which are received from the plurality ofinterfaces 19, 27, 35, 43, 51, 59, as shown in FIG. 5A, for example,with the frequency of the system clock SYCLK which is set higher thanthe frequency corresponding to the natural communication speeds onrespective interfaces. As the result of the frequency modulation, forexample, the digital data (DATA) shown in FIG. 5A are compressed on thetime base like digital data (compression DATA) shown in FIG. 5B, and thecompression data are then sent out to the data transfer line 3.

In the plurality of frequency demodulators (FDM) 17, 25, 33, 41, 49, 57,the frequency demodulation is executed to synchronize the compressiondata (Compression DATA) shown in FIG. 5B received via the data transferline 3, for example, with the natural communication speeds on theplurality of interfaces 19, 27, 35, 43, 51, 59. As the result of thefrequency demodulation, for example, the compression data (CompressionDATA) shown in FIG. 5B are expanded on the time base like the digitaldata (DATA) shown in FIG. 5A, and the expansion data are then receivedby the plurality of external devices 21, 29, 37, 45, 53, 61 via theplurality of interfaces 19, 27, 35, 43, 51, 59.

In the multiplexer (MUX) 11, the digital data are packetized by addingheader information (Header) including appropriately synchronizingsignal, sender, destination, acknowledge character (ACK), negativeacknowledge character (NAK), etc. to heads of the compression data(Compression DATA) transmitted from the plurality of interfaces 19, 27,35, 43, 51, 59, as shown in FIG. 5B, for example. The packetized digitaldata are multiplexed and then transmitted to the external network 13.

In the distributor (DMUX) 7, the header information of the packetizeddigital data received from the external network are interpreted, andthen the digital data are distributed by inverse multiplexing totransmit to the interfaces designated as the sender.

In turn, a second transmitter, a second receiver, a second communicationapparatus, and a communication method according to a second embodimentof the present invention will be explained with reference to FIGS. 6 to11 hereunder. In the second embodiment of the present invention, thereexist constituent members which are common to those of the above firstembodiment of the present invention. Hence, common references refer tothe common constituent members in both embodiments and therefore theirexplanations are omitted. Explanation of differences in structurebetween the first and second embodiments will be mainly made hereunder.

First, as shown in FIGS. 6 to 8, a second communication apparatus 101according to the second embodiment of the present invention isconstructed to include a second transmitter 102 and a second receiver104. The second communication apparatus 101 has a function ofimplementing the centralization process by which the digital data arecollected to the multiplexer and the distributor. More particularly, thecentralization process can be achieved by multiplexing the digital datawhich are transmitted from the plurality of external devicesrespectively, then transmitting multiplexed digital data to the externalnetwork installed in the vehicle, for example, then distributing themultiplexed digital data received from the external network by inversemultiplexing, and then receiving distributed digital data by theconcerned external device respectively, whereby the digital data havingtheir natural communication speeds specified based on the plurality ofprotocols can be collected to the multiplexer and the distributor. Theplurality of external devices are composed of a personal computer (PC),a telephone (TEL), etc., for example, and execute data exchange at theirnatural communication speeds which are specified based on mutuallydifferent protocols respectively.

Differences in structure between the second embodiment and the abovefirst embodiment of the present invention reside in that astar-configuration data transfer line is employed as the data transferline between the distributor (DMUX) 7 and the frequency demodulators(FDM) 17, 25, 33, 41, 49, 57 and between the multiplexer (MUX) 11 andthe frequency modulators (FM) 15, 23, 31, 39, 47, 55 and thatinformation adding portions (STAMP) 105, 107, 109, 111, 113, 115 foradding header information (Header), which include synchronizing signalspeculiar to respective interfaces, sender, destination, acknowledgecharacter (ACK), negative acknowledge character (NAK), etc.appropriately, to the output data output from respective interfaces areprovided between the frequency modulators (FM) 15, 23, 31, 39, 47, 55and the plurality of interfaces 19, 27, 35, 43, 51, 59.

Operations of the second transmitter, the second receiver, and thesecond communication apparatus constructed as above according to thesecond embodiment of the present invention will be explained hereunder.Since operations of the second transmitter 102 and the second receiver104 are included in the operation of the second communication apparatus101, their explanations are omitted hereunder.

According to the second communication apparatus 101 of the secondembodiment of the present invention, in order to transmit the digitaldata transmitted from the plurality of external devices 21, 29, 37, 45,53, 61 respectively to the external network, first of all, the headerinformation (Header) including synchronizing signals peculiar torespective interfaces, sender, destination, acknowledge character (ACK),negative acknowledge character (NAK), etc. appropriately are added torespective block data (I/F DATA), as shown in FIG. 9A, by informationadding portions (STAMP) 105, 107, 109, 111, 113, 115. The block data(I/F DATA) are transmitted from the plurality of interfaces 19, 27, 35,43, 51, 59 and are divided into plural blocks in a predetermined bitunit, for example, a 32-bit unit, in compliance with data formatspeculiar to respective interfaces. In order to add the headerinformation (Header) to the block data (I/F DATA), any informationadding scheme may be employed. For example, the header information(Header) may be added to heads of the block data (I/F DATA), otherwisethe header information (Header) may be added with the use of empty bitssuch as user areas in the block data (I/F DATA).

The block data (I/F DATA) to which the header information (Header) areadded are formed as data formats which have predetermined bit rates(bit/second) corresponding to natural communication speeds peculiar tothe plurality of interfaces 19, 27, 35, 43, 51, 59. The frequencymodulations are executed by respective frequency modulators (FM) 15, 23,31, 39, 47, 55 so as to synchronize the block data (I/F DATA), to whichthe header information (Header) are added, with the frequency ofpredetermined system clock of multiplexer side SYCLK in the multiplexer(MUX) 11 supplied from the clock generator (PLL/CG) 9. The digital datawhich are subjected to the frequency modulation, as shown in FIG. 9B,are then transmitted to the multiplexer (MUX) 11 via the data transferline 103 respectively.

When received the frequency-modulated digital data transmitted from theplurality of frequency modulators (FM) 15, 23, 31, 39, 47, 55respectively, the multiplexer (MUX) 11 then multiplexes by synchronizingthese digital data with the multiplexer side system clock SYCLK andtransmits the multiplexed digital data to the external network.

The multiplexed digital data (MUX DATA) multiplexed by the multiplexer(MUX) 11, as shown in FIG. 1A, are transformed into compression digitaldata (Compression MUX DATA) which are compressed on the time base byexecuting the frequency modulation to synchronize with the multiplexerside system clock SYCLK, then the synchronizing signals (SYNC) whichbeing in synchronism with the multiplexer side system clock SYCLK areadded to empty bit regions generated by such transformation, and thenthe multiplexed digital data (Compression MUX DATA) to which thesynchronizing signals (SYNC) are added, as shown in FIG. 10B, aretransmitted to the external network. In place of the case where themultiplexed digital data (Compression MUX DATA) to which thesynchronizing signals (SYNC) are added are transmitted, the blockdata(I/F DATA)to which the header information (Header) shown in FIG. 1Aare added may be transmitted to the external network. In this case,start position information indicating a head of block data may besupplemented into the header information (Header).

Modifications of the digital data by a series of above data processeswill be explained in more detail with reference to FIGS. 11A and 11B.Modifications are illustrated in FIG. 11A in which header information(Header) are added to respective heads of three types of block data 1 to3 being set to have mutually different bit lengths respectively. Anothermodifications are illustrated in FIG. 11B in which compression isapplied on the time base and the synchronizing signals (SYNC) are addedto three types of block data 1 to 3 with header information (Header).

In the meanwhile, in order to receive the digital data transmitted fromthe external network by the plurality of external devices 21, 29, 37,45, 53, 61 respectively, at first the distributor (DMUX) 7 receives themultiplexed digital data being transmitted from the external network,and then distributes the multiplexed digital data by inversemultiplexing in synchronism with the predetermined system clock ofdistributor side SYCLK in the distributor (DMUX) 7, interprets theheader information added to the distributed digital data to specify thesender, and then sends out predetermined digital data to respectiveexternal devices. Next, the plurality of frequency demodulators (FDM)17, 25, 33, 41, 49, 57 receive the digital data sent out from thedistributor (DMUX) 7 via the data transfer line 3, then executes thefrequency demodulation to synchronize the received digital data whichhave been synchronized with the frequency of the distributor side systemclock SYCLK with the natural communication speeds on the plurality ofinterfaces 19, 27, 35, 43, 51, 59, and then send out thefrequency-demodulated digital data to the plurality of interfaces 19,27, 35, 43, 51, 59 respectively. These digital data are then received bythe plurality of external devices 21, 29, 37, 45, 53, 61 via theplurality of interfaces 19, 27, 35, 43, 51, 59 respectively.

Mutually different frequencies may be employed as the predeterminedsystem clock of distributor side and the predetermined system clock ofmultiplexer side, while the mutually common frequency may also beemployed. In both cases, the centralization process can be implementedby collecting the digital data to the distributor (DMUX) 7 or themultiplexer (MUX) 11.

As still another modification of the second embodiment of the presentinvention, an information deleting portion for deleting the headerinformation (Header) may be supplemented to the digital data which arereceived from the distributor (DMUX) 7 via the data transfer line 103and to which the header information (Header) to allocate the pluralityof external devices 21, 29, 37, 45, 53, 61 as the senders are added. Inthis fashion, the plurality of external devices 21, 29, 37, 45, 53, 61can receive raw data without extra information after the headerinformation (Header) have been deleted.

As stated above, according to the second communication apparatus 101 ofthe second embodiment of the present invention, the centralizationprocess of digital data can be executed by concentrating the digitaldata, which being transmitted from the plurality of external devices 21,29, 37, 45, 53, 61 which can execute data exchange at their naturaltransmission speeds respectively or being transmitted from the externalnetwork, onto the distributor (DMUX) 7 or the multiplexer (MUX) 11, andalso smooth two-way communications between the external network and theplurality of external devices 21, 29, 37, 45, 53, 61 can be implemented.

Further, according to the second communication apparatus 101 of thesecond embodiment of the present invention, since the digital data beingcollected to the distributor (DMUX) 7 or the multiplexer (MUX) 11 aretransmitted in synchronism with the predetermined system clock in thedistributor (DMUX) 7 or the multiplexer (MUX) 11, any external deviceout of the plurality of external devices can access such digital data.Therefore, as will be described later, according to a fourthcommunication apparatus 202 of the fourth embodiment shown in FIG. 13,smooth two-way communications can be implemented between the pluralityof external devices in addition to the above two-way communicationsbetween the external network and the plurality of external devices.

Next, a third communication apparatus according to a third embodiment ofthe present invention will be explained with reference to FIG. 12hereunder. In the third embodiment of the present invention, there existconstituent members which are common to those of the above firstembodiment of the present invention. Therefore, common references referto the common constituent members in both embodiments and thereforetheir explanations are omitted. Explanation of differences in structurebetween the first and third embodiments will be mainly made hereunder.

The third embodiment is different from the first embodiment in that theplurality of external devices which execute data exchange at theircommunication speeds specified based on their own protocols have beenconnected to the first communication apparatus 1 according to the firstembodiment in structure, but a plurality of first to sixth externaldevices 213, 215, 217, 219, 221, 223 shown in FIG. 12 are connected tothe third communication apparatus 200 according to the third embodimentof the present invention to include the case where the first externaldevice 213 and the second external device 215 can communicate based on amutually common protocol, for example. In this case, a plurality offirst to sixth interfaces (I/F) 201, 203, 205, 207, 209, 211 whichconstitute a part of the communication apparatus 200 and employ theprotocols corresponding to the to-be-connected external devicesrespectively are connected.

Therefore, according to the third communication apparatus 200 of thethird embodiment of the present invention, as in the first embodiment,the digital data being multiplexed based on the time-division multiplexsystem on the common data transfer line 3, for example, are transmittedin synchronism with the predetermined system clock on the common datatransfer line 3, and therefore any external device out of the pluralityof external devices can access readily such digital data. In addition,since the plurality of interfaces (I/F) includes those employingmutually common protocols, smooth two-way communications can beimplemented easily between the plurality of external devices other thanthe above two-way communications between the external network and theplurality of external devices.

Subsequently, a fourth communication apparatus according to a fourthembodiment of the present invention will be explained with reference toFIG. 13 hereunder. In the fourth embodiment of the present invention,there exist constituent members which are common to those of the abovesecond embodiment of the present invention. Therefore, common referencesrefer to the common constituent members in both embodiments andtherefore their explanations are omitted. Differences in structurebetween the second and fourth embodiments will be mainly explainedhereunder.

The plurality of external devices which execute data exchange at theircommunication speeds specified based on their own protocols have beenconnected to the second communication apparatus 101 according to thesecond embodiment in structure, whereas the plurality of first to sixthexternal devices 213, 215, 217, 219, 221, 223 shown in FIG. 13 areconnected to the third communication apparatus 200 according to thethird embodiment of the present invention to include the case where thefirst external device 213 and the second external device 215 cancommunicate based on a mutually common protocol, for example. In thiscase, the plurality of first to sixth interfaces (I/F) 201, 203, 205,207, 209, 211 which constitute a part of the communication apparatus 200and employ the protocols corresponding to the to-be-connected externaldevices respectively are connected.

Hence, according to the fourth communication apparatus 202 of the fourthembodiment of the present invention, like the first embodiment, becausethe digital data being collected to the distributor (DMUX) 7 or themultiplexer (MUX) 11 are transmitted in synchronism with thepredetermined system clock in the distributor (DMUX) 7 or themultiplexer (MUX) 11, any external device out of the plurality ofexternal devices can access readily such digital data. Moreover, sincethe plurality of interfaces (I/F) includes those employing mutuallycommon protocols, smooth two-way communications can be implementedeasily between the plurality of external devices other than the abovetwo-way communications between the external network and the plurality ofexternal devices.

First to third communication systems according to fifth to seventhembodiments of the present invention will be explained in brief withreference to FIGS. 14 and 16 hereinbelow. In order to distinguish datacarrying medium provided in the inside of the above communicationapparatus from data carrying medium provided in the communicationsystem, the data carrying medium provided in the inside of thecommunication apparatus is called a data transfer line, while the datacarrying medium provided in the communication system is called a datatransmission line.

A first communication system 230 according to a fifth embodiment of thepresent invention is shown FIG. 14 wherein a plurality of communicationapparatuses 233, 233, . . . are connected via a bus-type datatransmission line 231. A second communication system 234 according to asixth embodiment of the present invention is shown in FIG. 15 wherein aplurality of communication apparatuses 233, 233, . . . are connected viaa star-configuration data transmission line 235 which is arranged aroundone centralized controller 239. A third communication system 236according to a seventh embodiment of the present invention is shown inFIG. 16 wherein a plurality of communication apparatuses 233, 233, . . .are connected via a ring-type data transmission line 237.

The first communication system 230 or the third communication system 236is so constructed that the plurality of communication apparatuses 233can access the data transmission lines 231 or 237 at natural timingperiods which are set in respective communication apparatuses 233 tosynchronize with the common system clock among the communicationapparatuses 233 upon data transmission. Therefore, in the firstcommunication system 230 or the third communication system 236, a newaccess control system is employed in which the timing periods peculiarto respective communication apparatuses 233 are set to be shiftedmutually such that the access issued from the plurality of communicationapparatuses 233 to the data transmission line 231 or 237 to transmit thedigital data are not simultaneously generated.

In particular, for example, in order to execute data exchange betweenthe sender communication apparatus and the destination communicationapparatus, at first a communication route is generated by establishing apredetermined timing clock used commonly between both communicationapparatuses, then the sender communication apparatus executes datatransmission in synchronism with a predetermined timing clock and thedestination communication apparatus executes data reception insynchronism with the predetermined timing clock.

Accordingly, the plurality of communication apparatuses 233 can accessthe data transmission lines 231, 237 in parallel respectively withavoiding collision of data. As a result, smooth two-way communicationsbetween any communication apparatuses can be realized while assuringexcellent real-time facility.

In the second communication system 234, the plurality of communicationapparatuses 233 are constructed so as to access the centralizedcontroller 239 at their timing periods peculiar to respectivecommunication apparatuses 233 in synchronism with the common systemclock among the plurality of communication apparatuses 233. Therefore,in this second communication system 234, a new access control scheme isemployed wherein the timing periods peculiar to respective communicationapparatuses 233 are set to be shifted mutually such that access to thecentralized controller 239 are not simultaneously generated from theplurality of communication apparatuses 233.

Accordingly, the plurality of communication apparatuses 233 can accessthe data transmission lines 231, 237 in parallel respectively withavoiding collision of data. Consequently, smooth two-way communicationsbetween any communication apparatuses can be realized while assuringexcellent real-time facility. In addition, the communication systemhaving a simple configuration to which the centralized controller andthe buffer memory for storing overflow data temporarily are not requiredcan be achieved.

The first to third communication systems 230, 234, 236 may beconstructed such that one or more than two external devices areconnected to the plurality of communication apparatuses respectively. Inthis case, the first to third communication systems 230, 234, 236 areable to exchange the digital data between any external devices, betweenany external device and any communication apparatus, or between anycommunication apparatuses.

Next, a fourth communication system according to an eighth embodiment ofthe present invention will be explained with reference to FIG. 17 inmore detail hereunder.

As shown in FIG. 17, the fourth communication system 301 according tothe eighth embodiment of the present invention is constructed byconnecting mutually a plurality of root hubs RH1, RH2, RH3, RH4, RH5serving as the communication apparatuses via a loop data transmissionline 303 to enable data exchange therebetween. A system control unit(SCU) 304 which can control and manage synchronization control ofoverall communication system 301, etc. is connected to the root hub RH1.As a network topology of the communication system 301, appropriate typesuch as bus type, or star type, for example, may be adopted in additionto the above loop type.

One or more than two external devices N1 to N15 are connected to theplurality of root hubs RH respectively. The plurality of root hubs RHare constructed so as to enable data exchange mutually between anyexternal devices N, between any root hubs RH, or between any externaldevice N and any root hub RH via the data transmission line 303. Variousexternal devices may be considered as the external devices N, forexample, a mobile telephone, a facsimile device (FAX), a digital TV set,a radio receiver, a navigation system (NV), a DVD-ROM drive, a CDplayer, a DAT (Digital Audio Taperecorder), an MD (Mini Disc) player, anaudio amplifier in which a digital signal processor (DSP) is built, aCAN (Controller Area Network) data bus, various sensors such as azimuthsensor, speed sensor, etc., a monitor device, a vehicle-equippedpersonal computer, and the like.

The plurality of root hubs RH are divided into respective functionalunits, for example, a tuner system for receiving radio waves such as TVor radio broadcast from the external devices N such as TV or radiostation; an amusement system to which sound signals, video signals,traffic snarl information, etc. are supplied from the external devices Nsuch as NV; a control system to which control information is suppliedfrom the external devices such as various sensors; an image signalsystem which supplies the image signals to the monitor devices, etc.; asound signal system which provides the sound signals to the audioamplifier which has the built-in digital signal processor (DSP), etc.

Specific device addresses such as RH1, RH2, . . . , RH5 are setindividually to respective root hubs RH previously, while specificdevice addresses such as N1, N2, . . . , N15 are set individually torespective external devices N previously. These specific deviceaddresses are used to designate the sender or the destination when dataexchange are executed between the root hubs RH, between the externaldevices N, or the external devices N and the root hubs RH via the datatransmission line 3.

Besides, device connection information storing devices (TCI) 305a, 305b,305c, 305d, 305e which are made up of microcomputers, for example, areconnected to the plurality of root hubs RH respectively. The deviceconnection information storing devices (TCI) 305 can store deviceconnection information in which types of the external devices N beingconnected to respective root hubs RH are correlated with I/F numbers 1,2, 3 of three device interfaces (abbreviated as "device I/F"hereinafter) which are connected to individual root hubs RH, forexample.

The device connection information stored in the device connectioninformation storing devices (TCI) 305 will be explained to take the roothub RH3 an example, for instance. The device connection information forthe root hub RH3 indicates that the DSP 1 (OUT) is connected to the I/Fnumber "1" of the root hub RH3, the CAN (IN) is connected to the I/Fnumber "2" of the root hub RH3, and the sensor 1 (IN) is connected tothe I/F number "3" of the root hub RH3. If the device connectioninformation are supplied to the root hubs RH respectively, types of theexternal devices N are being connected to individual root hubs RH can begrasped in respective root hubs RH.

Next, a fifth communication apparatus according to a ninth embodiment ofthe present invention will be explained with reference to FIG. 18hereunder, while illustrating the case where it is applied to thecommunication apparatus constituting the above fourth communicationsystem 301. In this case, the root hubs RH constituting the fourthcommunication system 301 shown in FIG. 17 corresponds to the fifthcommunication apparatus according to the ninth embodiment of the presentinvention.

In the fifth communication apparatus according to the ninth embodiment,there exist constituent members which are common to those of thecommunication apparatus according to the above first embodiment of thepresent invention shown in FIG. 1. Hence, common references refer to thecommon constituent members in both embodiments and therefore theirexplanations are omitted. Explanation of differences in structurebetween the first and ninth embodiments will be mainly made hereunder.

In addition to the configuration of the communication apparatus 1according to the first embodiment, the fifth communication apparatus 401according to the ninth embodiment of the present invention furthercomprises a device memory 403, a system memory 405 as an all deviceconnection information storing means, and a clock allocation portion 407as a clock allocation means. A master operation block 409 is composed ofthe system memory 405 and the clock allocation portion 407. This masteroperation block 409 is constructed to execute its function when thefifth communication apparatus 401 operates as the master communicationapparatus in the fourth communication system 301. In the fourthcommunication system 301, when one certain communication apparatusoperates as the master communication apparatus, other communicationapparatuses operate as slave communication apparatuses.

The device memory 403 has a function for storing the device connectioninformation which are acquired from the device connection informationstoring devices (TCI) 305 connected to own communication apparatus 401.The device connection information stored in the device memory 403 areread out by the multiplexer (MUX) 11, for example, and are then referredto in the multiplexer (MUX) 11 when sender addresses are added to thecommunication data transmitted from own communication apparatus 401 orthe external devices N connected to own communication apparatus 401, andforth.

The system memory 405 is constructed, as shown in FIG. 20, for example,to store the device connection information in all communicationapparatuses constituting the fourth communication system 301. In thedevice connection information, types of the external devices N which areconnected to the plurality of communication apparatuses respectively arecorrelated with the I/F numbers 1, 2, 3 of three devices I/F, forexample, which are installed in the communication apparatusesrespectively.

The clock allocation portion 407 is constructed to generate clockallocation information regarding appropriate distribution ratios of thecommon system clock SYCLK among the plurality of communicationapparatuses for respective external devices N, as shown in FIG. 22, forexample, based on the all device connection information, and then sendout the clock allocation information to the multiplexer (MUX) 11. Suchall device connection information are stored in the system memory 405and includes types and transmission capacities of the external deviceswhich are connected to the plurality of communication apparatusesconstituting the fourth communication system 301 respectively. When themultiplexer (MUX) 11 receives the clock allocation information, ittransmits the clock allocation information to all communicationapparatuses including own communication apparatus 401. Then, based onthe device reference clocks CK which are peculiar to various externaldevices N and are distributed at distribution radios of the system clockSYCLK in compliance with the clock allocation information, the pluralityof communication apparatuses including own communication apparatus 401can execute data exchange control between any senders and anydestinations, for example, the TEL/FAX (N1) and the DSP3 (N15).

The device reference clocks CK which are peculiar to various externaldevices N and are distributed at distribution radios of the system clockSYCLK in compliance with the clock allocation information will beexplained with reference to FIGS. 21A to 21K hereinbelow.

The system clock SYCLK is shown in FIG. 21A. First to eighth devicereference clocks CK1, CK2, . . . , CK8 which are generated byfrequency-dividing the system clock SYCLK appropriately are shown inFIGS. 21B to 21I, and ninth and tenth device reference clocks CK9, CK10which are generated by adding the device reference clocks CK beinggenerated by frequency-dividing the system clock SYCLK appropriately areshown in FIGS. 21J and 21K.

The first to third device reference clocks CK1, CK2, CK3 for threechannels are communication timing clocks which can be derived by 1/4frequency-dividing the system clock SYCLK. The device reference clocksCK1, CK2, CK3 are allocated to the external devices N such as theTEL/FAX, for example, which have a relatively high frequency of use.

The fourth device reference clock CK4 for one channel is a communicationtiming clock which can be derived by 1/8 frequency-dividing the systemclock SYCLK. The device reference clock CK4 is allocated to the externaldevices N such as various sensors, the CAN (Controller Area Network)data bus, the command dedicated clock used to transmit the command, forexample, which can be sufficiently operated at a relatively lowcommunication speed. As shown in FIG. 22, the fourth device referenceclock CK4 for one channel can be divided into plural subchannels byapplying suitable processes such as frequency division, addition, etc.to the fourth device reference clock CK4 for one channel, and then suchsubchannels can be allocated to respective sensors, the CAN data bus,etc. Since the device reference clocks are constructed to include thecommand dedicated clock used for transmitting the command, thecommunication system which is able to transmit the command from thesender to the destination can be implemented with a simple systemconfiguration.

In addition, the fifth to eighth device reference clocks CK5, CK6, CK7,CK8 for four channels are communication timing clocks which can bederived by 1/32 frequency-dividing the system clock SYCLK. The devicereference clocks CK1, CK2, CK3 are allocated to the external devices Nsuch as the CD player, the DAT, the MD player, the radio receiver, theNV (navigation) system, etc., for example.

The ninth device reference clock CK9 for one channel is a communicationtiming clock which can be generated by executing logical sum of thesecond device reference clock CK2 and the seventh device reference clockCK7. The ninth device reference clock CK9 is allocated to the externaldevices N such as the DVD-ROM drive, etc., for example.

The tenth device reference clock CK10 for one channel is a communicationtiming clock which can be generated by executing logical sum of thethird device reference clock CK3 and the eighth device reference clockCK8. The tenth device reference clock CK10 is allocated to the externaldevices N such as the digital TV set, etc., for example.

When the plurality of device reference clocks CK peculiar to variousexternal devices respectively are generated by distributing the systemclock SYCLK as described above, an important respect is that respectivepulse rising timings of the plurality of device reference clocks CK areset to be shifted among the external devices while considering the factthat pulse rising timings which serve as data communication timings ofrespective external devices N are not simultaneously generated among theexternal devices mutually. As the data communication timings of variousexternal devices N, pulse trailing timings may be employed instead ofpulse rising timings.

In this fashion, according to the fifth communication apparatus of theninth embodiment of the present invention, the clock allocationinformation concerning appropriate distribution ratios of the systemclock for respective external devices are generated based on the alldevice connection information, and the generated clock allocationinformation are transmitted to all communication apparatuses includingown communication apparatus. The all device connection information arestored in the all device connection information storing means andinclude types of the external devices connected to the plurality ofcommunication apparatuses constituting the communication systemrespectively. In response to the clock allocation information, theplurality of communication apparatuses including own communicationapparatus can execute data exchange control between any sender and anydestination, e.g., between the external devices, based on the devicereference clocks which are peculiar to various external devices anddistributed at distribution ratios of the system clock in compliancewith the clock allocation information.

Accordingly, communication data transmitted from various externaldevices are transmitted to the data transmission line respectively insynchronism with the communication timings in compliance with the devicereference clocks peculiar to respective external devices. In addition,pulse rising timings or pulse trailing timings which serve as thecommunication timings for the communication data being transmitted fromvarious external devices respectively are set to be shifted mutually.For this reason, communication data can be prevented beforehand frombeing transmitted simultaneously from different senders and thereforecollision between the communication data can be avoided firmly. As aresult, the communication apparatus which is able to contribute animprovement in communication efficiency of the communication system canbe realized.

According to the fourth communication system 301 in which the pluralityof communication apparatuses according to the eighth embodiment of thepresent invention are connected via the data transmission line,collision of the communication data can be surely avoided and as aresult the communication system which is able to improve thecommunication efficiency extremely can be implemented.

Next, a sixth communication apparatus according to a tenth embodiment ofthe present invention will be explained with reference to FIG. 19hereunder while illustrating the case where such communication apparatusis applied to the communication apparatus constituting the above fourthcommunication system 301. In this case, the root hubs RH constitutingthe fourth communication system 301 shown in FIG. 17 correspond to thecommunication apparatuses according to the tenth embodiment of thepresent invention.

In the sixth communication apparatus according to the tenth embodimentof the present invention, there exist constituent members which arecommon to those of the second communication apparatus according to thesecond embodiment shown in FIG. 6 and those of the fifth communicationapparatus according to the ninth embodiment shown in FIG. 18. Hence,since common references are assigned to the common constituent membersin the embodiments, their explanations are omitted. Explanation ofdifferences in structure between the tenth embodiment and the second andfifth embodiments will be mainly made hereunder.

In addition to the configuration of the communication apparatus 101according to the second embodiment, the sixth communication apparatus501 according to the ninth embodiment of the present invention furthercomprises the device memory 403, the system memory 405 as the all deviceconnection information storing means, and the clock allocation portion407 as the clock allocation means.

According to the sixth communication apparatus of the tenth embodimentof the present invention, like the fifth communication apparatus of theninth embodiment, the communication data being transmitted fromrespective external devices N are transmitted to the data transmissionline 303 in synchronism with the communication timings in compliancewith the device reference clocks CK peculiar to respective externaldevices. In addition, pulse rising timings or pulse trailing timingswhich serve as the communication timings for the communication databeing transmitted from various external devices N respectively are setto be shifted mutually. Therefore, communication data can be preventedin advance from being transmitted simultaneously from different sendersand therefore collision between the communication data can be avoidedfirmly. As a result, the communication apparatus which is able tocontribute an improvement in communication efficiency of thecommunication system can be realized.

According to the fourth communication system 301 in which the pluralityof communication apparatuses according to the eighth embodiment of thepresent invention are connected via the data transmission line,collision of the communication data can be surely avoided and as aresult the communication system which is able to improve thecommunication efficiency extremely can be implemented.

Though has been explained in detail, the present invention should not belimited to the above embodiments and other embodiments may beaccomplished by modifying the present invention appropriately.

That is to say, for example, various standards such as the IEEE1394, theUSB, etc. have been illustrated as the protocols for the interfacesbeing connected to the plurality of external devices in one-by-onecorrespondence in the communication apparatus of the embodiments of thepresent invention, but the present invention should not be limited tosuch instance. For example, the present invention can correspond to anyinterfaces based on the standards other than the protocols described inthe above embodiments.

Finally, although the case where the present invention is applied to thevehicle-equipped network has been illustrated in the above embodiments,the present invention is not limited to such case. Needless to say, thepresent invention may be applied to all types of the communicationsystems.

What is claimed is:
 1. A transmitter comprising:a data transfer line fortransferring digital data; a plurality of interfaces connected to aplurality of external devices in one-by-one correspondence, andconstructed so as to fit to transmission speeds peculiar to saidplurality of external devices respectively; a plurality of frequencymodulators connected to said plurality of interfaces in one-by-onecorrespondence, for executing a frequency modulation to synchronize saiddigital data which have natural transmission speeds on respectiveinterfaces with a predetermined system clock on said data transfer line,and then sending out said digital data which are subjected to saidfrequency modulation to said data transfer line respectively; amultiplexer for multiplexing said digital data which are transmittedfrom said plurality of frequency modulators via said data transfer linein synchronism with said predetermined system clock, and thentransmitting multiplexed digital data to an external network; and aclock generator for generating reference clocks including saidpredetermined system clock, and then supplying said reference clocks tosaid plurality of frequency modulators and said multiplexerrespectively.
 2. A receiver comprising:a data transfer line fortransferring digital data; a distributor for receiving multiplexeddigital data transmitted from an external network, and then distributingsaid multiplexed digital data by inverse multiplexing in synchronismwith a predetermined system clock on said data transfer line to send outto said data transfer line; a plurality of interfaces connected to aplurality of external devices in one-by-one correspondence, andconstructed so as to fit to transmission speeds peculiar to saidplurality of external devices respectively; a plurality of frequencydemodulators for receiving digital data output from said distributor viasaid data transfer line, then executing a frequency demodulation tosynchronize input data which have been synchronized with saidpredetermined system clock on said data transfer line with said naturaltransmission speeds on said plurality of interfaces respectively, andthen sending out said digital data which are subjected to said frequencydemodulation to said plurality of interfaces respectively; and a clockgenerator for generating reference clocks including said predeterminedsystem clock, and then supplying said reference clocks to saiddistributor and said plurality of frequency demodulators respectively.3. A communication apparatus comprising:a data transfer line fortransferring digital data; a distributor for receiving multiplexeddigital data transmitted from an external network, and then distributingsaid multiplexed digital data by inverse multiplexing in synchronismwith a predetermined system clock on said data transfer line to send outto said data transfer line; a plurality of interfaces connected to aplurality of external devices in one-by-one correspondence, andconstructed so as to fit to transmission speeds peculiar to saidplurality of external devices respectively; a plurality of frequencymodulators connected to said plurality of interfaces in one-by-onecorrespondence, for executing a frequency modulation to synchronize saiddigital data which have natural transmission speeds on respectiveinterfaces with a predetermined system clock on said data transfer line,and then sending out said digital data which are subjected to saidfrequency modulation to said data transfer line respectively; aplurality of frequency demodulators for receiving said digital dataoutput from said distributor via said data transfer line, then executinga frequency demodulation to synchronize input digital data which havebeen synchronized with said predetermined system clock on said datatransfer line with said natural transmission speeds on said plurality ofinterfaces respectively, and then sending out said digital data whichare subjected to said frequency demodulation to said plurality ofinterfaces respectively; a multiplexer for multiplexing said digitaldata which are transmitted from said plurality of frequency modulatorsvia said data transfer line in synchronism with said predeterminedsystem clock, and then transmitting multiplexed digital data to anexternal network; and a clock generator for generating reference clocksincluding said predetermined system clock, and then supplying saidgenerated reference clocks to said distributor, said multiplexer, saidplurality of frequency modulators, and said plurality of frequencydemodulators respectively.
 4. A communication method for use in acommunication system including,a data transfer line for transferringdigital data, and a plurality of interfaces connected to a plurality ofexternal devices in one-by-one correspondence, and constructed so as tofit to transmission speeds peculiar to said plurality of externaldevices respectively, said communication method comprising the steps of:executing a frequency modulation to synchronize said digital data whichare output from said plurality of external devices having naturaltransmission speeds on said plurality of interfaces respectively with apredetermined system clock on said data transfer line, and then sendingout said digital data which are subjected to said frequency modulationto said data transfer line respectively; andmultiplexing said digitaldata which are input via said data transfer line respectively insynchronism with said predetermined system clock, and then transmittingmultiplexed digital data to an external network; whereby said digitaldata transmitted from said plurality of external devices respectivelyare sent to said external network via said data transfer line, andreceiving multiplexed digital data transmitted from said externalnetwork, and then distributing said multiplexed digital data by inversemultiplexing in synchronism with said predetermined system clock to sendout to said data transfer line; receiving said digital data transmittedvia said data transfer line respectively, and then executing a frequencydemodulation to synchronize said digital data which have beensynchronized with said predetermined system clock with said naturaltransmission speeds on said plurality of interfaces respectively; andreceiving said digital data which are subjected to said frequencydemodulation by said plurality of external devices via said plurality ofinterfaces respectively; whereby said multiplexed digital datatransmitted from said external network are received by said plurality ofexternal devices via said data transfer line respectively.
 5. Acommunication method according to claim 4, wherein said digital datainput via said data transfer line respectively are transformed intoplural packets and then transmitted to said external network on atime-division multiplex basis.
 6. A transmitter according to claim 1,further comprising a plurality of information adding means for addingheader information including at least destination to said digital datawhich are divided into a predetermined proper unit with respect to saidplurality of interfaces and then output.
 7. A receiver according toclaim 2, further comprising a plurality of header information deletingmeans for deleting header information from said digital data to whichsaid header information including at least destination are added andwhich are sent out from said distributor via said data transfer line. 8.A communication apparatus according to claim 3, further comprising:aplurality of information adding means for adding header informationincluding at least destination to said digital data which are dividedinto a predetermined proper unit with respect to said plurality ofinterfaces and then output; and a plurality of header informationdeleting means for deleting said header information from said digitaldata to which said header information including at least destination areadded and which are sent out from said distributor via said datatransfer line.
 9. A communication apparatus according to claim 3,wherein data exchanges are executed between senders and destinationsbased on device reference clocks peculiar to said plurality of externaldevices which are distributed at predetermined distribution ratios ofsaid predetermined system clock.
 10. A transmitter comprising:a datatransfer line for transferring digital data; a plurality of interfacesconnected to a plurality of external devices in one-by-onecorrespondence, and constructed so as to fit to transmission speedspeculiar to said plurality of external devices respectively; a pluralityof frequency modulators connected to said plurality of externalinterfaces in one-by-one correspondence, for executing a frequencymodulation to synchronize said digital data which have naturaltransmission speeds on respective interfaces with a predetermined systemclock of multiplexer side, and then sending out said digital data whichare subjected to said frequency modulation to said data transfer linerespectively; a multiplexer for multiplexing said digital data which aretransmitted from said plurality of frequency modulators via said datatransfer line in synchronism with said predetermined system clock ofmultiplexer side, and then transmitting multiplexed digital data to anexternal network; and a clock generator for generating reference clocksincluding said predetermined system clock and then supplying saidgenerated reference clocks to said plurality of frequency modulators andsaid multiplexer respectively.
 11. A receiver comprising:a data transferline for transferring digital data; a distributor for receivingmultiplexed digital data transmitted from an external network, and thendistributing said multiplexed digital data by inverse multiplexing insynchronism with a predetermined system clock of distributor side insaid data transfer line to send out to said data transfer line; aplurality of interfaces connected to a plurality of external devices inone-by-one correspondence, and constructed so as to fit to transmissionspeeds peculiar to said plurality of external devices respectively; aplurality of frequency demodulators for receiving said digital dataoutput from said distributor via said data transfer line, then executinga frequency demodulation to synchronize said digital data which havebeen synchronized with said predetermined system clock of distributorside with said natural transmission speeds on said plurality ofinterfaces respectively, and then sending out said digital data whichare subjected to said frequency demodulation to said plurality ofinterfaces respectively; and a clock generator for generating referenceclocks including said predetermined system clock of distributor side,and then supplying said reference clocks to said distributor and saidplurality of frequency demodulators respectively.
 12. A communicationapparatus comprising:a data transfer line for transferring digital data;a distributor for receiving multiplexed data transmitted from anexternal network, and then distributing multiplexed digital data byinverse multiplexing in synchronism with a predetermined system clock ofdistributor side to send out to said data transfer line; a plurality ofinterfaces connected to a plurality of external devices in one-by-onecorrespondence, and constructed so as to fit to transmission speedspeculiar to said plurality of external devices respectively; a pluralityof frequency modulators connected to said plurality of interfaces inone-by-one correspondence, for executing a frequency modulation tosynchronize said digital data which have natural transmission speeds onrespective interfaces with a predetermined system clock of multiplexerside, and then sending out said digital data which are subjected to saidfrequency modulation to said data transfer line respectively; aplurality of frequency demodulators for receiving said digital datawhich are output from said distributor via said data transfer line, thenexecuting a frequency demodulation to synchronize said digital datawhich have been synchronized with said predetermined system clock ofdistributor side with said natural transmission speeds on said pluralityof interfaces respectively, and then sending out said digital data whichare subjected to said frequency demodulation to said plurality ofinterfaces respectively; a multiplexer for multiplexing said digitaldata which are transmitted from said plurality of frequency modulatorsvia said data transfer line in synchronism with said predeterminedsystem clock of multiplexer side, and then transmitting multiplexeddigital data to an external network; and a clock generator forgenerating reference clocks including said predetermined system clock ofdistributor side and said predetermined system clock of multiplexerside, and then supplying said reference clocks to said distributor, saidmultiplexer, said plurality of frequency modulators, and said pluralityof frequency demodulators respectively.
 13. A communication method foruse in a communication system including,a data transfer line fortransferring digital data, and a plurality of interfaces connected to aplurality of external devices in one-by-one correspondence, andconstructed so as to fit to transmission speeds peculiar to saidplurality of external devices respectively, said communication methodcomprising the steps of:executing a frequency modulation to synchronizesaid digital data which are output from said plurality of externaldevices having said natural transmission speeds on said plurality ofinterfaces respectively with a predetermined system clock of multiplexerside, and then sending out said digital data which are subjected to saidfrequency modulation to said data transfer line respectively; andmultiplexing said digital data which are input via said data transferline respectively in synchronism with said predetermined system clock ofmultiplexer side, and then transmitting multiplexed digital data to anexternal network; whereby said digital data which are transmitted fromsaid plurality of external devices respectively are sent to saidexternal network via said data transfer line, and receiving saidmultiplexed digital data transmitted from said external network, andthen distributing said multiplexed digital data by inverse multiplexingin synchronism with said predetermined system clock of distributor sideto send out to said data transfer line; receiving said digital datatransmitted via said data transfer line respectively, and then executinga frequency demodulation to synchronize said digital data which havebeen synchronized with said predetermined system clock of distributorside with said natural transmission speeds on said plurality ofinterfaces respectively; and receiving said digital data which aresubjected to said frequency demodulation by said plurality of externaldevices via said plurality of interfaces respectively; whereby saidmultiplexed digital data which are transmitted from said externalnetwork are received by said plurality of external devices via said datatransfer line respectively.
 14. A communication method according toclaim 13, wherein said digital data which are input via said datatransfer line respectively are transformed into plural packets and thentransmitted to said external network on a time-division multiplex basis.15. A communication apparatus according to claim 12, wherein dataexchanges are executed between senders and destinations based on devicereference clocks peculiar to said plurality of external devices whichare distributed at predetermined distribution ratios of saidpredetermined system clock.
 16. A communication apparatus according toclaim 12, wherein said multiplexer side system clock and saiddistributor side system clock are set mutually at a common frequency.17. A communication method according to claim 13, wherein saidmultiplexer side system clock and said distributor side system clock areset mutually at a common frequency.
 18. A transmitter according to claim10, further comprising a plurality of information adding means foradding header information including at least destination to said digitaldata which are divided into a predetermined proper unit with respect tosaid plurality of interfaces and then output.
 19. A receiver accordingto claim 11, further comprising a plurality of header informationdeleting means for deleting header information from said digital data towhich said header information including at least destination are addedand which are sent out from said distributor via said data transferline.
 20. A communication apparatus according to claim 12, furthercomprising:a plurality of information adding means for adding headerinformation including at least destination to said digital data whichare divided into a predetermined proper unit with respect to saidplurality of interfaces and then output; and a plurality of headerinformation deleting means for deleting said header information fromsaid digital data to which said header information including at leastsaid destination are added and which are sent out from said distributorvia said data transfer line.
 21. A communication method for use in acommunication system including,a data transfer line for transferringdigital data, and a plurality of interfaces connected to a plurality ofexternal devices in one-by-one correspondence, and constructed so as tofit to transmission speeds peculiar to said plurality of externaldevices respectively, said communication method comprising the stepsof:adding header information including at least destination to saiddigital data which have natural communication speeds on said pluralityof interfaces and are divided into a predetermined proper unit of saidplurality of interfaces and then output; executing a frequencymodulation to synchronize said digital data to which said headerinformation are added with a predetermined system clock of multiplexerside, and then sending out said digital data which are subjected to saidfrequency modulation to said data transfer line respectively; andmultiplexing said digital data which are input via said data transferline respectively in synchronism with said predetermined system clock ofmultiplexer side, and then transmitting multiplexed digital data to anexternal network; whereby said digital data which are transmitted fromsaid plurality of external devices respectively are sent to saidexternal network via said data transfer line, and receiving saidmultiplexed digital data transmitted from said external network, andthen distributing said multiplexed digital data by inverse multiplexingin synchronism with a predetermined system clock of distributor side tosend out to said data transfer line; receiving said digital data whichare transmitted via said data transfer line respectively, and thenexecuting a frequency demodulation to synchronize said digital datawhich have been synchronized with said predetermined system clock ofdistributor side with said natural transmission speeds on said pluralityof interfaces respectively; and receiving said digital data which aresubjected to said frequency demodulation by said plurality of externaldevices via said plurality of interfaces respectively; whereby saidmultiplexed digital data which are transmitted from said externalnetwork are received by said plurality of external devices via said datatransfer line respectively.
 22. A communication method for use in acommunication system including,a data transfer line for transferringdigital data, and a plurality of interfaces connected to a plurality ofexternal devices in one-by-one correspondence, and constructed so as tofit to transmission speeds peculiar to said plurality of externaldevices respectively, said communication method comprising the stepsof:executing a frequency modulation to synchronize said digital datawhich have natural communication speeds on said plurality of interfaceswith a predetermined system clock of multiplexer side; adding headerinformation including at least destination to said digital data whichare subjected to said frequency modulation and are divided into apredetermined proper unit of said plurality of interfaces and thenoutput respectively, and then sending out said digital data to whichsaid header information are added to said data transfer linerespectively; and multiplexing said digital data which are input viasaid data transfer line respectively in synchronism with saidpredetermined system clock of multiplexer side, and then transmittingmultiplexed digital data to an external network; whereby said digitaldata which are transmitted from said plurality of external devicesrespectively are sent to said external network via said data transferline, and receiving said multiplexed digital data transmitted from saidexternal network, and then distributing said multiplexed digital data byinverse multiplexing in synchronism with a predetermined system clock ofdistributor side to send out to said data transfer line; receiving saiddigital data which are transmitted via said data transfer linerespectively, and then executing a frequency demodulation to synchronizesaid digital data which have been synchronized with said predeterminedsystem clock of distributor side with said natural transmission speedson said plurality of interfaces respectively; and receiving said digitaldata which are subjected to said frequency demodulation by saidplurality of external devices via said plurality of interfacesrespectively; whereby said multiplexed digital data which aretransmitted from said external network are received by said plurality ofexternal devices via said data transfer line respectively.